Methods for forward error correction coding above a radio link control layer and related apparatus

ABSTRACT

Transmission techniques are provided that improve service continuity and reduce interruptions in delivery of content that can be caused by transitions that occur when the User Equipment (UE) moves from one cell to the other, or when the delivery of content changes from a Point-to-Point (PTP) connection to a Point-to-Multipoint (PTM) connection in the same serving cell, and vice-versa. Such transmission techniques enable seamless delivery of content across cell borders and/or between different transmission schemes such as Point-to-Multipoint (PTM) and Point-to-Point (PTP). Mechanisms for adjusting different streams and for recovering content from each data block during such transitions are also provided so that data is not lost during a transition. In addition, mechanisms for realigning data during decoding at a receiving terminal are also provided.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

The present application for patent claims priority to ProvisionalApplication No. 60/497,457 entitled “Method and Apparatus for SeamlessDelivery of Broadcast and Multicast Content Across Cell Borders and/orBetween Different Transmission Schemes” filed Aug. 21, 2003 andProvisional Application No. 60/497,456 entitled “L2 Design for OuterCoding Scheme” filed Aug. 21, 2003, both of which can be assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND

1. Field

The present invention relates generally to communication systems, andmore specifically to delivery of broadcast and multicast content.

2. Background

Wireless communication systems have traditionally been used to carryvoice traffic and low data rate non-voice traffic. Today wirelesscommunication systems are being implemented that also carry high datarate (HDR) multimedia traffic, such as video, data, and other types oftraffic. Multimedia Broadcast and Multicast Service (MBMS) channels maybe used to transmit streaming applications based on voice, audio andvideo data sources such as, radio broadcasts, television broadcasts,movies, and other types of audio or video content. Streaming datasources can tolerate delay and a certain amount of loss or bit errors,since these sources are sometimes intermittent and typically compressed.As such, the data-rate of transmissions arriving at the Radio AccessNetwork (RAN) can be highly variable. Because application buffers aretypically finite, the MBMS transmission mechanisms are needed thatsupport variable source data-rates.

Base stations typically provide such multimedia traffic services to thesubscriber stations by transmitting an information signal that can beoften organized into a plurality of packets. A packet may be a group ofbytes, including data (payload) and control elements, that are arrangedinto a specific format. The control elements may comprise, for example,a preamble and a quality metric that can include a cyclical redundancycheck (CRC), parity bit(s), and other types of metrics. The packets areusually formatted into a message in accordance with a communicationchannel structure. The message travels between the origination terminaland the destination terminal, and can be affected by characteristics ofthe communication channel, such as, signal-to-noise ratio, fading, timevariance, and other such characteristics. Such characteristics canaffect the modulated signal differently in different communicationchannels. Among other considerations, transmission of a modulatedinformation signal over a wireless communication channel requiresselection of appropriate methods for protecting the information in themodulated signal. Such methods may comprise, for example, encoding,symbol repetition, interleaving, and other methods known to one ofordinary skill in the art. However, these methods increase overhead.Therefore, an engineering compromise between reliability of messagedelivery and the amount of overhead must be made.

The operator typically selects either a Point-to-Point (PTP) connectionor a Point-to-Multipoint (PTM) connection on a cell by cell basisdepending on the number of subscriber stations or User Equipment (UE)interested in receiving the MBMS content.

Point-to-Point (PTP) transmission uses dedicated channels to send theservice to selected users in the coverage area. A “dedicated” channelcarries information to/from a single subscriber station. InPoint-to-Point (PTP) transmissions a separate channel can be used fortransmission to each mobile station. Dedicated user traffic for one userservice in the forward link or downlink direction can be sent, forexample, through a logical channel called the Dedicated Traffic Channel(DTCH). Point-to-Point (PTP) communication services are typically mostefficient, for example, if there are not enough users demanding aspecific Multimedia Broadcast and Multicast Service (MBMS) in thecoverage area. In such cases, Point-to-Point (PTP) transmission may beused in which the base station transmits the service only to thespecific users who have requested the service. For example, in WCDMAsystems it can be more efficient to use a dedicated channel orPoint-to-Point (PTP) transmission until there are more than apredetermined number of mobile stations.

A “broadcast communication” or “Point-to-Multipoint (PTM) communication”is a communication over a common communication channel to a plurality ofmobile stations. A “common” channel carries information to/from multiplesubscriber stations, and may be simultaneously used by severalterminals. In a Point-to-Multipoint (PTM) communication service, acellular base station may broadcast multimedia traffic service on acommon channel if, for example, the number of users demanding theservice exceeds a predetermined threshold number within the coveragearea of the base station. In CDMA 2000 systems, broadcast orPoint-to-Multipoint (PTM) transmission is typically used in lieu of thePtP transmission, since the PtM radio bearer is almost as efficient asthe PtP radio bearer. Common channel transmissions from a particularbase station may not necessarily be synchronized with common channeltransmissions from other base stations. In a typical broadcast systemone or more central stations serve content to a (broadcast net ofusers). The central station(s) can transmit information to either allsubscriber stations or to a specific group of subscriber stations. Eachsubscriber station interested in a broadcast service monitors a commonforward link signal. Point-to-Multipoint (PTM) transmissions can be senton a downlink or forward common channel. This common broadcast forwardlink signal is typically broadcast on a unidirectional channel, such asthe Common Traffic Channel (CTCH) that exists in the forward link or“downlink” direction. Because this channel is unidirectional, thesubscriber station generally does not communicate with the base stationsince allowing all subscriber units to communicate back to the basestation might overload the communication system. Thus, in the context ofPoint-to-Multipoint (PTM) communication services, when there is an errorin the information received by the subscriber stations, the subscriberstations may not be able to communicate back to the base station.Consequently, other means of information protection can be desirable.

In CDMA 2000 systems, the subscriber station can soft combine inPoint-to-Multipoint (PTM) transmission. Even when steps are taken toprotect the information signal, the conditions of the communicationchannel can degrade such that the destination station cannot decode someof the packets transferred over dedicated channels. In such cases, oneapproach can be to simply re-transmit the non-decoded packets using anAutomatic Retransmission reQuest (ARQ) made by the destination(subscriber) station to the origination (base) station. Retransmissionhelps ensure delivery of the data packet. In the event the data can notbe delivered correctly, the user of RLC at the transmitting side can benotified.

The subscriber station typically undergoes transitions in a number ofscenarios. These transitions can be classified in different ways. Forexample, transitions may be classified as “cross transitions” and“direct transitions.” Transitions can also be classified as “inter-cell”transitions and “intra-cell” transitions.

Transitions between cells or transmission schemes can result in serviceinterruption that can be undesirable to users. Problems may arise whenthe subscriber station or User Equipment (UE) moves from one cell to theother or when the delivery of Multimedia Broadcast and Multicast Service(MBMS) content changes from one mode to another mode in the servingcell. Transmissions from neighboring cells may be time-shifted withrespect to one another by an amount Δt1. Moreover, additional delay canbe introduced during a transition since the mobile station needs todetermine system information in the target cell, which requires acertain amount of processing time Δt2. The data streams transmitted fromdifferent cells (or different transport channel types Point-to-Point(PTP)/Point-to-Multipoint (PTM)) may be offset relative to one another.Therefore, during Point-to-Multipoint (PTM) transmissions from differentcells, the mobile station may receive the same block of content twice orsome blocks of content may be lost, which can be undesirable in terms ofQuality of Service. Transitions between cells and/or betweenPoint-to-Point (PTP) transmission and Point-to-Multipoint (PTM)transmission could cause an interruption in service, depending on theduration of the transition and on the delay or misalignment betweentransmissions.

There is therefore a need in the art for transmission techniques thatwill provide service continuity and reduce interruptions in delivery ofcontent that can be caused by transitions that occur when the UserEquipment (UE) moves from one cell to the other, or caused bytransitions that occur when the delivery of content changes from aPoint-to-Point (PTP) connection to a Point-to-Multipoint (PTM)connection in the same serving cell, and vice-versa. Such transmissiontechniques would preferably enable seamless delivery of content acrosscell borders and/or between different transmission schemes such asPoint-to-Multipoint (PTM) and Point-to-Point (PTP). Mechanisms foradjusting different streams and for recovering content from each datablock during such transitions are also desirable so that data is notlost during a transition. It would also be desirable to providemechanisms for realigning data during decoding at a receiving terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a communication system.

FIG. 2 is a block diagram of the UMTS signaling protocol stack.

FIG. 3 is a block diagram of a packet switched user plane of the UMTSprotocol stack.

FIG. 4 is a block diagram of an access stratum portion of the UMTSsignaling protocol stack.

FIG. 5A is a block diagram of data transfer modes used in the Radio LinkControl (RLC) layer of the UMTS signaling protocol stack, and variouschannels used in each layer.

FIG. 5B is a block diagram showing the architecture of the Radio LinkControl (RLC) layer including various RLC data transfer modes.

FIG. 5C is a block diagram showing an entity for implementing the RadioLink Control (RLC) Acknowledged Mode (AM).

FIG. 6 is a diagram of a modified UMTS protocol stack having a ForwardError Correction Layer.

FIG. 7A shows an embodiment of a protocol structure of the accessstratum that includes a forward error correction (FEC) layer.

FIG. 7B shows another embodiment of a protocol structure of the accessstratum that includes a forward error correction (FEC) layer.

FIG. 8 is a diagram of an information block and outer code blockcorresponding to the information block.

FIG. 9A is a diagram showing an outer code block structure that can beapplied to Multimedia Broadcast and Multicast Service (MBMS) data.

FIG. 9B is a diagram showing the outer code block structure of FIG. 9Ain which multiple rows are sent per Transmission Time Interval (TTI).

FIG. 9C is a diagram showing the outer block structure of FIG. 9A inwhich each row is sent in multiple TTIs.

FIGS. 10A and 10B are diagrams that show the outer code blocks generatedby the Forward Error Correction layer.

FIG. 11 is an embodiment of a Forward Error Correction (FEC) layer usedin a RLC UM+ entity.

FIG. 12A shows an encoding process for creating an outer code block fromdata units in which row sizes of the outer code block are fixed.

FIG. 12B shows an example of information transmitted over the air inFIG. 12A.

FIG. 13 shows an encoding process for creating an outer code blockhaving a variable row size.

FIG. 14 is a diagram of an embodiment of a Forward Error Correction(FEC) header format.

FIG. 15 is an algorithm for enabling mobile stations to delay decodingby the time-offset between different logical streams.

FIG. 16 is a diagram that shows a temporal relationship between outercode blocks received by a mobile station as the mobile stationtransitions between receiving a Point-To-Multipoint (PTM) transmissionfrom cell A and another Point-To-Multipoint (PTM) transmission from cellB.

FIG. 17 is a diagram that shows a temporal relationship between outercode blocks received by a mobile station as a transition between aPoint-To-Multipoint (PTM) transmission and a Point-To-Point (PTP)transmission occurs.

FIG. 18 is a diagram that shows a temporal relationship between outercode blocks received by a mobile station during a transition orrelocation between a Point-To-Point (PTP) transmission from RadioNetwork Controller (RNC) A and another Point-To-Point (PTP) transmissionfrom Radio Network Controller (RNC) B.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

The term “mobile station” is used herein interchangeably with the terms“destination station,” “subscriber station,” “subscriber unit,”“terminal” and “User Equipment (UE),” and is used herein to refer to thehardware, such as a base station, with which an access network, such asthe UMTS Terrestrial Radio Access Network (UTRAN), communicates. In UMTSsystems, the User Equipment (UE) is a device that allows a user toaccess UMTS network services and also preferably includes a USIM thatcontains all of a user's subscription information. A mobile station maybe mobile or stationary, and can generally include any communicator,data device or terminal that communicates through a wireless channel orthrough a wired channel, for example, using fiber optic or coaxialcables. Mobile stations may be embodied in devices that include but thatare not limited to PC card, compact flash, external or internal modem,or wireless or wireline phone.

The term “connection setup state” refers to the state in which a mobilestation is in the process of establishing an active traffic channelconnection with a base station.

The term “traffic state” refers to the state in which a mobile stationhas established an active traffic channel connection with a basestation.

The term “communication channel” is used herein to mean a physicalchannel or a logical channel in accordance with the context.

The term “physical channel” is used herein to refer to a channel thatcarries user data or control information over the air interface.Physical channels are the “transmission media” that provide the radioplatform through which the information is actually transferred, andserve to carry signaling and user data over the radio link. A physicalchannel typically comprises the combination of frequency scrambling codeand channelization code. In the uplink direction, relative phase can bealso included. A number of different physical channels can be used inthe uplink direction based upon what the mobile station is attempting todo. In a UMTS system, the term physical channel may also refer to thedifferent kinds of bandwidth allocated for different purposes over a Uuinterface. The physical channels form the physical existence of the Uuinterface between the User Equipment (UE) domain and the network accessdomain. Physical channels can be defined by physical mappings andattributes used to transfer data over the air interface.

The term “transport channel” is used herein to refer to a communicationroute for data transport between peer physical layer entities. Transportchannels relate to the manner in which information is transmitted.Generally, there can be two types of transport channels known as CommonTransport Channels and Dedicated Transport Channels. A transport channelcan be defined by how and with what characteristics data can betransferred over the air interface on the physical layer, for example,whether using dedicated or common physical channels, or multiplexing oflogical channels. Transport channels may serve as service access points(SAPs) for the physical layer. In a UMTS system, the transport channeldescribes how the logical channels can be transferred and maps theseinformation flows to physical channels. Transport channels can be usedto carry signaling and user data between the Medium Access Control (MAC)layer and the Physical Layer (L1). The Radio Network Controller (RNC)sees transport channels. Information passes to the physical layer fromthe MAC layer over any one of a number of transport channels that can bemapped to physical channels.

The term “logical channel” is used herein to refer to an informationstream dedicated to the transfer of a specific type of information orthe radio interface. Logical channels relate to the information beingtransmitted. A logical channel can be defined by what type ofinformation is transferred, for example, signaling or user data, and canbe understood as different tasks the network and terminal should performat different point in time. Logical channels can be mapped intotransport channels performing actual information transfer between themobile station domain and the access domain. Information passes vialogical channels that can be mapped through transport channels which canbe mapped to physical channels.

The term “dedicated channel” is used herein to refer to a channel thatis typically dedicated to, or reserved for, a specific user, and thatcarries information to or from a specific mobile station, subscriberunit, or user equipment. A dedicated channel typically carriesinformation intended for a given user, including data for the actualservice as well as higher layer control information. A dedicated channelcan be identified by a certain code on a certain frequency. A dedicatedchannel can be bi-directional to potentially allow for feedback.

The term “common channel” is used herein to refer to a transport channelthat carries information to/from multiple mobile stations. In a commonchannel information may be shared among all mobile stations. A commonchannel can be divided between all users or a group of users in a cell.

The term “Point-to-Point (PTP) communication” is used herein to mean acommunication transmitted over a dedicated, physical communicationchannel to a single mobile station.

The terms “broadcast communication” or “Point-to-Multipoint (PTM)communication” can be used herein to refer to a communication over acommon communication channel to a plurality of mobile stations.

The term “reverse link or uplink channel” is used herein to refer to acommunication channel/link through which the mobile station sendssignals to a base station in the radio access network. This channel mayalso be used to transmit signals from a mobile station to a mobile basestation or from a mobile base station to a base station.

The term “forward link or downlink channel” is used herein to mean acommunication channel/link through which a radio access network sendssignals to a mobile station.

The term “Transmission Timing Interval” (TTI) is used herein to refer tohow often data arrives from higher layers to the physical layer. ATransmission Timing Interval (TTI) may refer to the inter-arrival timeof a Transport Block Set (TBS), and is approximately equal to theperiodicity at which a TBS is transferred by the physical layer on theradio interface. Data sent on a Transport Channel during a TTI can becoded and interleaved together. A TTI can span multiple radio frames,and can be a multiple of the minimum interleaving period. The startpositions of the TTIs for different transport channels that can bemultiplexed together for a single connection are time aligned. TTIs havea common starting point. The Medium Access Control delivers oneTransport Block Set to the physical layer every TTI. Different transportchannels mapped on the same physical channel can have differentTransmission Timing Interval (TTI) durations. Multiple PDUs can be sentin one TTI.

The term “packet” is used herein to mean a group of bits, including dataor payload and control elements, arranged into a specific format. Thecontrol elements may comprise, for example, a preamble, a qualitymetric, and others known to one skilled in the art. Quality metriccomprises, for example, a cyclical redundancy check (CRC), a parity bit,and others known to one skilled in the art.

The term “access network” is used herein to mean equipment necessary foraccessing the network. The access network may comprise a collection ornetwork of base stations (BS) and one or more base station controllers(BSC). The access network transports data packets between multiplesubscriber stations. The access network may be further connected toadditional networks outside the access network, such as a corporateintranet or the Internet, and may transport data packets between accessterminals and such outside networks. In the UMTS system the accessnetwork can be referred to as the UMTS Terrestrial Radio Access Network(UTRAN).

The term “core network” is used herein to refer to the switching androuting capability for connecting to either the Public SwitchedTelephone Network (PSTN), for circuit switched calls in the circuitswitched (CS) domain, or the Packet Data Network (PSDN) forpacket-switched calls in the packet switched (PS) domain. The term “corenetwork” also refers to the routing capability for mobility andsubscriber location management and for authentication services. The corenetwork includes network elements needed for switching and subscribercontrol.

The term “base station” is used herein to refer to an “originationstation” that includes the hardware with which mobile stationcommunicates. In the UMTS system, the term “node B” can be usedinterchangeably with the term “base station.” A base station may befixed or mobile.

The term “cell” is used herein to refer to either hardware or ageographic coverage area depending on the context in which the term isused.

The term “Service Data Unit (SDU)” is used herein to refer to a dataunit exchanged with the protocol sitting above the protocol of interest.

The term “Payload Data Unit (PDU)” is used herein to refer to a dataunit exchanged with the protocol sitting below the protocol of interest.If the identity of the protocol of interest is ambiguous, then aspecific mention will be made in the name. For example, FEC-PDUs are thePDUs of the FEC layer.

The term “soft handoff” is used herein to mean a communication between asubscriber station and two or more sectors, wherein each sector belongsto a different cell. The reverse link communication can be received byboth sectors, and the forward link communication can be simultaneouslycarried on the two or more sectors' forward links.

The term “softer handoff” is used herein to mean a communication betweena subscriber station and two or more sectors, wherein each sectorbelongs to the same cell. The reverse link communication can be receivedby both sectors, and the forward link communication can besimultaneously carried on one of the two or more sectors' forward links.

The term “erasure” is used herein to mean failure to recognize a messageand can also be used to refer to a set of bits which can be missing atthe time of decoding.

The term “cross transition” may be defined as a transition fromPoint-to-Point (PTP) transmission to Point-to-Multipoint (PTM)transmission, or vice-versa. The four possible cross transitions arefrom Point-to-Point (PTP) transmission in cell A to Point-to-Multipoint(PTM) transmission in cell B, from Point-to-Multipoint (PTM)transmission in cell A to Point-to-Point (PTP) transmission in cell B,from Point-to-Point (PTP) transmission in cell A to Point-to-Multipoint(PTM) transmission in cell A, and from Point-to-Multipoint (PTM)transmission in cell A to Point-to-Point (PTP) transmission in cell A.

The term “direct transition” may be defined as transitions from onePoint-to-Point transmission to another Point-to-Point transmission andtransitions from Point-to-Multipoint transmission to Point-to-Multipointtransmission. The two possible direct transitions are fromPoint-to-Point (PTP) in cell A to Point-to-Point (PTP) transmission incell B, and from Point-to-Multipoint (PTM) transmission in cell A toPoint-to-Multipoint (PTM) transmission in cell B.

The term “inter-cell transition” is used to refer to a transition acrosscell boundaries. The four possible inter-cell transitions are fromPoint-to-Point (PTP) transmission in cell A to Point-to-Point (PTP)transmission in cell B, from Point-to-Multipoint (PTM) transmission incell A to Point-to-Multipoint (PTM) transmission in cell B, fromPoint-to-Point (PTP) transmission in cell A to Point-to-Multipoint (PTM)transmission in cell B, and from Point-to-Multipoint (PTM) transmissionin cell A to Point-to-Point (PTP) transmission in cell B. Generally, themost frequent transition is the Point-to-Multipoint (PTM) transmissionto Point-to-Multipoint (PTM) transmission across cell boundaries.

The term “intra-cell transition” is used to refer to transitions withina cell from one mode to another mode. The two possible intra-celltransitions are from Point-to-Point (PTP) transmission in cell A toPoint-to-Multipoint (PTM) transmission in cell A, and fromPoint-to-Multipoint (PTM) transmission in cell A to Point-to-Point (PTP)transmission in cell A.

The term “radio bearer” is used to refer to a service provided by Layer2 for transfer of user data between User Equipment (UE) and the UMTSTerrestrial Radio Access Network (UTRAN).

Embodiments of the invention will now be discussed in which aspectsdiscussed above are implemented in a WCDMA or UMTS communicationssystem. FIGS. 1-5C explain some aspects of a conventional UMTS or WCDMAsystem in which aspects of the inventions described herein could beapplied in this description is provided only for purposes ofillustration and limitation. It should be appreciated that aspects ofthe invention can also be applicable in other systems carrying bothvoice and data such as GSM systems and CDMA 2000 systems conforming tothe “3rd Generation Partnership Project” (3GPP), embodied in a set ofdocuments including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 PhysicalLayer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000standard), and GSM specifications such as TS 04.08 (the Mobile radiointerface layer 3 specification), TS 05.08 (Radio Subsystem LinkControl), and TS 05.01 (Physical Layer on the Radio Path (GeneralDescription)).

For example, although the description specifies that the radio accessnetwork 20 can be implemented using the Universal Terrestrial RadioAccess Network (UTRAN) air interface, alternatively, in a GSM/GPRSsystem, the access network 20 could be a GSM/EDGE Radio Access Network(GERAN), or in an inter-system case it could be comprise cells of aUTRAN air interface and cells of a GSM/EDGE air interface.

UMTS Network Topology

FIG. 1 is a block diagram of a communication system according to theUMTS network topology. A UMTS system includes User Equipment (UE) 10, anaccess network 20, and a core network 30. The UE 10 is coupled to theaccess network which is coupled to the core network 30 which can becoupled to an external network.

The UE 10 includes mobile equipment 12 and a Universal SubscriberIdentity Module (USIM) 14 that contains a user's subscriptioninformation. The Cu interface not shown) is the electrical interfacebetween the USIM 14 and the mobile equipment 12. The UE 10 is generallya device that allows a user to access UMTS network services. The UE 10may be a mobile such as a cellular telephone, a fixed station, or otherdata terminal. The mobile equipment may be, for an example, a radioterminal used for radio communications over an air interface (Uu). TheUu interface is the interface through which the UE accesses the fixedpart of the system. The USIM is generally an application that resides ona “smartcard” or other logic card that includes a microprocessor. Thesmart card holds the subscriber identity, performs authenticationalgorithms, and stores authentication in encryption keys andsubscription information needed at the terminal.

The access network 20 includes the radio equipment for accessing thenetwork. In a WCDMA system, the access network 20 is the UniversalTerrestrial Radio Access Network (UTRAN) air interface. The UTRANincludes at least one Radio Network Subsystem (RNS) that includes atleast one base station or “node B” 22 coupled to at least one RadioNetwork Controller (RNC) 24.

The RNC controls the radio resources of the UTRAN. The RNCs 24 of theaccess network 20 communicate with the core network 30 via the Iuinterface. The Uu interface, Iu interface 25, Iub interface, and Iurinterface allow for internetworking between equipment from differentvendors and are specified in the 3GPP standards. Implementation of theRadio Network Controller (RNC) varies from vendor to vendor, andtherefore will be described in general terms below.

The Radio Network Controller (RNC) 24 serves as the switching andcontrolling element of the UMTS Terrestrial Radio Access Network(UTRAN), and is located between the Iub interface and Iu interface 25.The RNC acts as a service access point for all services the UTRANprovides to the core network 30, for example, management of connectionsto the user equipment. The Iub interface 23 connects a node B 22 and anRadio Network Controller (RNC) 24. The Iu interface connects the UTRANto the core network. The Radio Network Controller (RNC) provides aswitching point between the Iu bearer and the base stations. The UserEquipment (UE) 10 may have several radio bearers between itself and theRadio Network Controller (RNC) 24. The radio bearer is related to theUser Equipment (UE) context which is a set of definitions required bythe Iub in order to arrange common connections and dedicated connectionsbetween the User Equipment (UE) and Radio Network Controller (RNC). Therespective RNCs 24 may communicate with each other over an optional Iurinterface that allows soft handover between cells connected to differentnodes 22. The Iur interface thus allows for inter-RNC connections. Insuch cases, a serving RNC maintains the Iu connection 25 to the corenetwork 30 and performs selector and outer loop power control functions,while a drift RNC transfers frames that can be exchanged over the Iurinterface to mobile station 10 via one or more base stations 22.

The RNC that controls one node B 22 can be referred to as thecontrolling RNC of the node B, and controls the load and congestion ofits own cells, and also executes admission control and code allocationsfor new radio links to be established in those cells.

RNCs and base stations (or node Bs) can be connected via and communicateover the Iub interface 23. The RNCs control use of the radio resourcesby each base station 22 coupled to a particular RNC 24. Each basestation 22 controls one or more cells and provides a radio link to themobile station 10. The base station may perform interface processingsuch as channel coding and interleaving, rate adaptation and spreading.The base station also performs basic radio resource managementoperations such as the interloop power control. The base station 22converts the data flow between the Iub and Uu interfaces 23, 26. Thebase station 22 also participates in radio resources management. Anover-the air interface Uu 26 couples each base station 22 to the mobilestation 10. The base stations can be responsible for radio transmissionin one or more cells to the mobile station 10, and for radio receptionin one or more cells from the mobile station 10.

The core network 30 includes all of the switching and routing capabilityfor (1) connecting to either the PSTN 42 if a circuit switched call ispresent or to a Packet Data Network (PDN) is a packet-switched call ispresent, (2) mobility and subscriber location management, and (3)authentication services. The core network 30 can include a home locationregister (HLR) 32, a mobile switching services center/visitor locationregister (MSC/VLR) 34, a gateway mobile switching center (GMSC) 36, aserving general packet radio service support node (SGSN) 38, and agateway GPRS support node (GGSN) 40.

The core network 30 may be coupled to an external circuit-switched (CS)network 42 that provides circuit-switched connections, such as PublicSwitched Telephone Network (PSTN) or (ISDN), if a packet switched callis present, or may be coupled to a PS network 44, such as the Internet,that provides connections for packet data services if a packet switchedcall is present.

UMTS Signaling Protocol Stack

FIG. 2 is a block diagram of the IMTS signaling protocol stack 110. TheUMTS signaling protocol stack 110 includes an access stratum and anon-access stratum (NAS).

The access stratum typically includes a physical layer 120, layer 2 130which includes a medium access control (MAC) layer 140 and a radio linkcontrol (RLC) layer 150, and a radio resource control (RRC) layer 160.The various layers of the access stratum will be described in greaterdetail below.

The UMTS non-access stratum layer is essentially the same as GSM upperlayers and can be divided into a circuit switched portion 170 and apacket switched portion 180. The circuit switched portion 170 includes aconnection management (CM) layer 172 and a mobility management (MM)layer 178. The CM layer 172 handles circuit-switched calls and includesvarious sublayers. The call control (CC) sublayer 174 executes functionssuch as establish and release. The supplementary services (SS) sublayer176 executes functions such as call forwarding and three-way calling. Ashort message services (SMS) sublayer 177 executes short messageservices. The MM layer 178 handles location updating and authenticationfor circuit-switched calls. The packet switched portion 180 includes asession management (SM) sublayer 182 and a GPRS mobility management(GMM) sublayer 184. The session management (SM) sublayer 182 handlespacket-switched calls by executing functions such as establish andrelease, and also includes a short message services (SMS) section 183.The GMM sublayer 184 handles location updating and authentication forpacket-switched 1 alls.

FIG. 3 is a block diagram of a packet switched user plane of the UMTSprotocol stack. The stack includes an access stratum (AS) layer and anon-access stratum (NAS) layer. The NAS layer includes the applicationlayer 80 and the Packet Data Protocol (PDP) layer 90. The applicationlayer 80 is provided between the User Equipment (UE) 10 and the remoteuser 42. The PDP layer 90, such as IP or PPP, is provided between theGGSN 40 and the User Equipment (UE) 10. Lower layer packet protocols(LLPP) 39 are provided between the remote user 42 and the SGSN 38. Iuinterface protocols 25 are provided between the Radio Network Controller(RNC) 24 and the SGSN 38, and Iub interface protocols are providedbetween the Radio Network Controller (RNC) 24 and node B 22. Otherportions of the AS layer will be described below.

Access Stratum (AS) Layer

FIG. 4 is a block diagram of the access stratum portion of the UMTSsignaling protocol stack. The conventional access stratum includes thephysical layer (L1) 120, the data link layer (L2) 130 having sublayersincluding Medium Access Control (MAC) layer 140, Radio Link Control(RLC) layer 150, Packet Data Convergence Protocol (PDCP) layer 156,Broadcast/Multicast Control (BMC) layer 158, and a Radio ResourceControl (RRC) layer 160. These layers will be further described below.

Radio bearers carry user data 163 between application layers and layertwo (L2) 130. The control plane signaling 161 can be used for all UMTSspecific control signaling, and includes the application protocol in thesignaling bearer for transporting the application protocol messages. Theapplication protocol can be used for setting up bearers to the UE 10.The user plane transports all user plane information 163 sent andreceived by the user such as a coded voice in a voice call or thepackets in an internet connection. The user plane information 163carries the data stream and the data bearers for those data streams.Each data stream can be characterized by one or more frame protocolsspecified for that interface.

The Radio Resource Control (RRC) layer 160 functions as the overallcontroller of the access stratum, and configures all other layers in theaccess stratum. The RRC layer 160 generates control plane signaling 161that controls the Radio Link Control Units 152, the physical layer (L1)120, the Medium Access Control (MAC) layer 140, the Radio Link Control(RLC) layer 150, the Packet Data Convergence Protocol (PDCP) layer 156,and the Broadcast/Multicast Control (BMC) layer 158. The Radio ResourceControl (RRC) layer 160 determines the types of measurements to make,and reports those measurements. The RRC layer 160 also serves as thecontrol and signaling interface to the non-access stratum.

More specifically, the RRC layer 160 broadcasts system informationmessages that include both access stratum and non-access stratuminformation elements to all User Equipment (UE) 10. The RRC layer 160establishes, maintains, and releases a Radio Resource Control (RRC)connection between the UTRAN 20 and the UE 10. The UE RRC requests theconnection, whereas the UTRAN RRC sets up and releases the connection.The RRC layer 160 also establishes, reconfigures, and releases RadioBearers between the UTRAN 20 and the UE 10, with the UTRAN 20 initiatingthese operations.

The RRC layer 160 also handles various aspects of User Equipment (UE) 10mobility. These procedures depend on the UE State, whether the call is acircuit switched or packet switched call, and the Radio AccessTechnology (RAT) of the new cell. The RRC layer 160 also pages the UE10. The UTRAN RRC pages the UE regardless of whether the UE is listeningto the paging channel or the paging indicator channel. The UE's RRCnotifies the upper layers of the core network (CN) 30.

Data link layer (L2) 130 includes a Medium Access Control (MAC) sublayer40, a Radio Link Control (RLC) sublayer 150, a Packet Data ConvergenceProtocol (PDCP) sublayer 156, and a Broadcast/Multicast Control (BMC)sublayer 158.

The broadcast and multicast control protocol (BMC) 158 covnveys, overthe radio interface, messages originating from the cell broadcast centerby adapting broadcast/multicast service originating from the broadcastdomain on the radio interface. The BMC protocol 158 offers a servicecalled “a radio bearer,” and exists in the user plane. The BMC protocol158 and RNC store the cell broadcast messages received over the CBC-RNCinterface for scheduled transmission. On the UTRAN side, the BMC 158calculates the required transmission rate for the cell broadcast servicebased on the messages that can be received over the CBC-RNC interface(not shown) and requests appropriate CTCH/FACH resources from the RRC.The BMC protocol 158 also receives scheduling information together witheach cell broadcast message over the CBC-RNC interface. Based on thisscheduling information, on the UTRAN side the BMC generates scheduledmessages and scheduled BMC message sequences accordingly. On the userequipment side, the BMC evaluates the schedule messages and indicatesthe scheduling parameters to the RRC which can be then used by the RRCto configure the lower layers for discontinuous reception. The BMC alsotransmits the BMC messages, such as scheduling and cell broadcastmessages according to a schedule. Non-corrupted cell broadcast messagescan be delivered to the upper layer. Part of the control signalingbetween the UE 10 and the UTRAN 20 can be Radio Resource Control (RRC)160 messages that carry all parameters required to set up, modify andrelease layer 2 protocol 130 and layer 1 protocol 120 entities. RRCmessages carry in their payload all of the higher layer signaling. TheRadio Resource Control (RRC) controls the mobility of user equipment inthe connected mode by signaling such as measurements, handovers and cellupdates.

The Packet Data Convergence Protocol (PDCP) 156 exists in the user planefor services from the PS domain. Services offered by the PDCP can becalled radio bearers. The Packet Data Convergence Protocol (PDCP)provides header compression services. The Packet Data ConvergenceProtocol (PDCP) 156 contains compression methods that can provide betterspectral efficiency for services transmitting IP packets over the radio.Any of several header compression algorithms can be utilized. The PDCPcompresses redundant protocol information at the transmitting entity anddecompresses at the receiving entity. The header compression method canbe specific to the particular network layer, transport layer, or upperlayer protocol combinations, for example, TCP/IP and RTP/UDP/IP. ThePDCP also transfers user data that it receives in the form of a PDCPService Data Units (SDU) from the non-access stratum and forwards themto the RLC entity, and vice versa. The PDCP also provides support forlossless SRNS relocation. When the PDCP uses an Acknowledged Mode (AM)RLC with in sequence delivery, PDCP entities which can be configured tosupport losses RSRNS relocation have Protocol Data Unit (PDU) sequencenumbers, which together with unconfirmed PDCP packets can be forwardedto the new SRNC during relocation.

The RLC layer 150 offers services to higher layers (e.g., the non accessstratum) via service access points (SAPs) which can be used by higherlayer protocols in the UE side and by the IURNAP protocol in the UTRANside. Service access points (SAPS) describe how the RLC layer handlesthe data packets. All higher layer signaling, such as mobilitymanagement, call control, session management etc., can be encapsulatedin RLC messages for transmission of the radio interface. The RLC layer150 includes various Radio Link Control Entities 152 coupled to the MAClayer 140 via logical channels that carry the signaling information anduser data.

On the control plane 161, the RLC services can be used by the RLC layerfor signaling transport. On the user plane 163, the RLC services can beused either by the service specific protocol layers PDCP or BMC or byother higher layer user plane functions. The RLC services can be calledsignaling radio bearers in the control plane 161 and radio bearers inthe user plane 163 for services that do not utilize the PDCP 156 or userplane protocols. In other words, the RLC layer 150 provides services inthe control plane 161 called signaling radio bearers (SRBs), and in theuser plane 163 provides services called a radio bearers (RBs) if thePDCP and BMC protocols can not be used by that service. Otherwise, theRB service can be provided by the PDCP layer 156 or BMC layer 158.

The Radio Link Control (RLC) layer 150 performs framing functions touser and control data, that include segmentation/concatenation andpadding functionality. The RLC layer 150 typically provides segmentationand retransmission services to the Radio Resource Control (RRC) 160layer for control data in the control plane 161 and to the applicationlayer for user data in the user plane 163. The RLC layer typicallyperforms segmentation/reassembly of variable length higher layerProtocol Data Units (PDUs) into/from smaller RLC Protocol Data Units(PDUs). One Radio Link Control (RLC) Protocol Data Unit (PDU) typicallycarries one PDU. The Radio Link Control (RLC) PDU size can be set, forexample, according to the smallest possible bit rate for the serviceusing the Radio Link Control (RLC). As will be discussed below, forvariable rate services, several Radio Link Control (RLC) PDUs can betransmitted during one transmission time interval (TTI) when any bitrate higher than the lowest one it used. The RLC transmitting entityalso performs concatenation. If the contents of a Radio Link Control(RLC) Service Data Unit (SDU) do not fill an integer number of RadioLink Control (RLC) PDUs, the first segment of the next Radio LinkControl (RLC) SDU may be put into the Radio Link Control (RLC) PDU inconcatenation with the last segment of the previous RLC SDU. The RLCtransmitting entity also typically performs a padding function. When theremaining data to be transmitted does not fill an entire Radio LinkControl (RLC) PDU of a given size, the remainder of that data field canbe filled with padding bits. According to aspects of the inventiondiscussed below with reference to FIGS. 11-13, for example, techniquescan be provided for reducing or eliminating the amount of padding thatis utilized.

The RLC receiving entity detects duplicates of received Radio LinkControl (RLC) PDUs and ensures that the result in the higher layer PDUis delivered once to the upper layer. The RLC layer also controls therate at which the PRLC transmitting entity may send information to anRLC receiving entity.

FIG. 5A is a block diagram of that illustrates the data transfer modesused in the Radio Link Control (RLC) layer of the UMTS signalingprotocol stack, and that shows possible mappings of logical, transportand physical UMTS channels with respect to the access stratum. Oneskilled in the art will appreciate that all mappings would notnecessarily be defined at the same time for a given User Equipment (UE),and multiple instantiations of some mappings may occur simultaneously.For example, a voice call might use three Dedicated Traffic Channel(DTCH) logical channels mapped to three Dedicated Channel (DCH)transport channels. Moreover, some channels shown in FIG. 5, such asCPICH, SCH, DPCCH, AICH and PICH, exist in the physical layer context,and do not carry upper layer signaling or user data. The contents ofthese channels can be defined at the physical layer 120 (L1).

Each RLC instance in the Radio Link Control (RLC) layer can beconfigured by the Radio Resource Control (RRC) layer 160 to operate inone of three modes: the transparent mode (TM), unacknowledged mode (UM),or acknowledged mode (AM), which are described in detail below withreference to FIG. 5B. The three data transfer modes indicate the mode inwhich the Radio Link Control (RLC) is configured for a logical channel.The transparent and unacknowledged mode RLC entities are defined to beunidirectional whereas the acknowledged mode entities arebi-directional. Normally, for all RLC modes, the CRC error detection isperformed on the physical layer and the result of the CRC check isdelivered to the RLC together with the actual data. Depending on thespecific requirements of each mode, these modes perform some or all ofthe functions of the RLC layer 150, which include segmentation,reassembly, concatenation, padding, retransmission control, flowcontrol, duplicate detection, in-sequence delivery, error correction andciphering. These functions are described in more detail below withreference to FIGS. 5B and 5C. According to an aspect of the inventiondiscussed herein, a new Radio Link Control (RLC) data transfer mode canbe provided.

The MAC layer 140 offers services to the RLC layer 150 by means oflogical channels that are characterized by the type of data transmitted.The Medium Access Control (MAC) layer 140 maps and multiplexes logicalchannels to transport channels. The MAC layer 140 identifies the UserEquipment (UE) that are on common channels. The MAC layer 140 alsomultiplexes/demultiplexes higher layer PDUs into/from transport blocksdelivered to/from the physical layer on common transport channels. TheMAC handles service multiplexing for common transport channels since itcan not be done in the physical layer. When a common transport channelcarries data from dedicated type logical channels, the Medium AccessControl (MAC) header includes an identification of the UE. The MAC layeralso multiplexes and demultiplexes higher layer PDUs into/from transportblock sets delivered to or from the physical layer on dedicatedtransport channels.

The MAC layer 140 receives RLC PDUs together with status information onthe amount of data in the RLC transmission buffer. The MAC layer 140compares the amount of data corresponding to the transport channel withthresholds set by the RRC layer 160. If the amount of data is too highor too low, then the MAC sends a measurement report on traffic volumestatus to the RRC. The RRC layer 160 can also request that the MAC layer160 sends these measurements periodically. The RRC layer 160 uses thesereports for triggering reconfiguration of the radio bearers and/ortransport channels.

The MAC layer also selects an appropriate transport format (TF) for eachtransport channel depending on the instantaneous source rates of thelogical channels. The MAC layer 140 provides priority handling of dataflows by selecting “high bit rate” and “low bit rate” transport formats(TFs) for different data flows. Packet switched (PS) data is inherentlybursty, and thus the amount of data available to send varies from frameto frame. When more data is available, the MAC layer 140 may choose oneof the higher data rates, however, when both signaling and user data areavailable the MAC layer 140 chooses between them to maximize the amountof data sent from the higher priority channel. The transport format (TF)can be selected with respect to the transport format combinations (TFCs)which can be defined by admission control for each connection.

The Medium Access Control (MAC) layer also performs ciphering. Eachradio bearer can be ciphered separately. The ciphering details aredescribed in the 3GPP TS 33.102.

In a system such as WCDMA there are three types of transport channelsthat can be used to transmit packet data. These channels are known as acommon transport channel, a dedicated transport channel, and a sharedtransport channel. In the downlink, the transport channel packet data isselected by a packet scheduling algorithm. In the uplink, the transportchannel is selected by the mobile 10 based on the parameters set by thepacket scheduling algorithm.

Common channels can be, for example, the random access channel RACH inthe uplink and the forward access channel FACH in the downlink. Bothcarry signaling data and user data. Common channels have a low set uptime. Because common channels can be used for signaling beforeconnections are set up, common channels can be used to send packetsimmediately without any long set up time. There are typically a few RACHor FACH per sector. Common channels do not have a feed back channel andtherefore typically use open loop power control or fixed power.Moreover, common channels can not use soft handover. Thus, the linklevel performance of common channels can be worse than that of dedicatedchannels and more interference can be generated than with dedicatedchannels. Consequently, common channels can be more suitable fortransmitting small individual packets. Applications to be used in commonchannels would be applications such as short message services, and shorttext emails. Sending a single request to a web page could also fit wellinto the concept of common channels however in the case of larger dataamounts, common channels suffer from poor radio performance.

Dedicated channels can use fast power control and soft handover featuresthat improve radio performance, and less interference is typicallygenerated than with the common channels. However, setting up a dedicatedchannel takes more time than accessing common channels. Dedicatedchannels can have variable bit rates from a few kilobytes per second upto 2 megabytes per second. Because the bit rate changes duringtransmission, the downlink orthogonal code must be allocated accordingto the highest bit rate. Therefore, the variable bit rate dedicatedchannels consume valuable downlink orthogonal code space.

The physical layer (L1) 120 couples to the MAC layer 140 via transportchannels that carry signaling information and user data. The physicallayer 120 offers services to the MAC layer via transport channels thatcan be characterized by how and with what characteristics data istransferred.

The physical layer (L1) 120 receives signaling and user data over theradio link via physical channels. The physical layer (L1) typicallyperforms multiplexing and channel coding including CRC calculation,forward-error correction (FEC), rate matching, interleaving transportchannel data, and multiplexing transport channel data, as well as otherphysical layer procedures such as acquisition, access, page, and radiolink establishment/failure. The physical layer (L1) may also beresponsible for spreading and scrambling, modulation, measurements,transmit diversity, power weighting, handover, compressed mode and powercontrol.

FIG. 5B is a block diagram showing the architecture of the Radio LinkControl (RLC) layer. As mentioned above, each RLC entity or instance 152in the Radio Link Control (RLC) layer 150 can be configured by the RadioResource Control (RRC) layer 160 to operate in one of three datatransfer modes: the transparent mode (TM), unacknowledged mode (UM), oracknowledged mode (AM). The data transfer mode for the user data can becontrolled by a Quality of Service (QoS) setting.

The TM is unidirectional and includes a transmitting TM entity 152A andan receiving TM entity 152B. In transparent mode no protocol order isadded to higher layer data. Erroneous protocol data units (PDUs) can bediscarded or marked erroneous. Streaming type transmission can be usedin which higher layer data is typically not segmented, though in specialcases, transmissions of limited segmentations/reassembly capability canbe accomplished. When segmentation/reassembly is used, it can benegotiated in the radio bearer set up procedure.

The UM is also unidirectional and includes a transmitting UM entity 152Cand a receiving UM entity 152D. An UM RLC entity is defined asunidirectional because no association between the uplink and downlink isneeded. Data delivery is not guaranteed in UM. The UM can be used, forexample, for certain RRC signaling procedures where the acknowledgmentand retransmissions are not part of the RRC procedure. Examples of userservices that utilize the unacknowledged mode RLC are the cell broadcastservice and voice over IP. Received erroneous data can be either markedor discarded depending on the configuration. A timer-based discardwithout explicit signaling function can be applied, thus RLC PDUs whichcan not be transmitted within a specified time can simply be removedfrom the transmission buffer. In the unacknowledged data transfer mode,the PDU structuring includes sequence numbers, and a sequence numbercheck can be performed. The sequence number check helps guarantee theintegrity of reassembled PDUs and provides a means of detectingcorrupted Radio Link Control (RLC) SDUs by checking the sequence numberin Radio Link Control (RLC) PDUs when they are reassembled into a RadioLink Control (RLC) SDU. Any corrupted Radio Link Control (RLC) SDUs canbe discarded. Segmentation and concatenation can also be provided in theUnacknowledged Mode (UM).

In acknowledged mode, RLC AM entity is bi-directional and capable ofpiggybacking an indication of the status of the link in the oppositedirection into user data. FIG. 5C is a block diagram showing an entityfor implementing the Radio Link Control (RLC) Acknowledged Mode (AM)entity and how an AM PDU can be constructed. Data packets (RLC SDUs)received from higher layers via AM-SAP can be segmented and/orconcatenated 514 to Protocol Data Units (PDU) of a fixed length. Thelength of the Protocol Data Unit is a semi-static value decided in theradio bearer set up, and can be changed through the RRC radio bearerreconfiguration procedure. For concatenation or padding purposes, bitscarrying information on the length and extension can be inserted intothe beginning of the last Protocol Data Unit or data from an SDU can beincluded. If several SDUs fit into one PDU, they can be concatenated inthe appropriate length indicators (LIs) can be inserted in the beginningof the PDU. The PDUs can be then placed in the transmission buffer 520,which can also take care of retransmission management.

The PDU can be constructed by taking one PDU from the transmissionbuffer 520, adding a header for it, and if the data in the PDU does notfill the whole RLC PDU, a padding field or piggyback status message canbe appended. The piggyback status message can originate either from thereceiving side 530 or from the transmitting side 510 to indicate anRLCSDU discard. The header contains the RLC PDU sequence number (SN), apollbit (P), which can be used to request status from the peer entity,and optionally a length indicator (LI) which can be used ifconcatenation of SDUs, padding, or a piggyback PDU takes place in theRLC PDU.

The Acknowledged Mode (AM) is typically used for packet type services,such as internet browsing and email downloading. In the acknowledgedmode, an automatic repeat request (ARQ) mechanism can be used for errorcorrection. Any received packets with errors can be retransmitted. Thequality versus delay performance of the RLC can be controlled by the RRCthrough configuration of a number of retransmissions provided by theRLC. If the RLC can not deliver the data correctly, for example, if themaximum number of retransmission has been reached or the transmissiontime has been exceeded, then the upper layer is notified and the RadioLink Control (RLC) SDU can be discarded. The peer entity can also beinformed of the SDU discard operation by sending a move receiving windowcommand in a status message so that also the receiver removes all PDUsbelonging to the discarded Radio Link Control (RLC) SDU.

The RLC can be configured for both in-sequence and out-of-sequencedelivery. With in-sequence delivery the order of the higher layer ofPDUs can be maintained, whereas out-of-sequence delivery forwards higherlayer PDUs as soon as they are completely received. The RLC layerprovides in sequence delivery of higher layer PDUs. This functionpreserves the order of higher layer PDUs that were submitted fortransfer by the RLCs. If this function is not used, out of sequencedelivery can be provided. In addition to data PDU delivery, status andreset control procedures can be signaled between peer RLC entities. Thecontrol procedures can even use a separate logical channel, thus, one AMRLC entity can either use one or two logical channels.

Ciphering can be performed in the RLC layer for acknowledged andunacknowledged RLC modes. In FIG. 5C, the AM RLC PDU is ciphered 540,excluding the two first two bits which comprise the PDU sequence numberand the pollbit. The PDU sequence number is one input parameter to theciphering algorithm, and it must be readable by the peer entity toperform the ciphering. The 3GPP specification TS33.102 describesciphering.

The PDU can be then forwarded to the MAC layer 140 via logical channels.In FIG. 5C, extra logical channels (DCCH/DTCH) are indicated by dashlines which illustrate that one RLC entity can be configured to send thecontrol PDUs and data PDUs using different logical channels. The receiveside 530 of the AM entity receives RLC AM PDUs through one of thelogical channels from the MAC layer. Errors can be checked with thephysical layer CRC which can be calculated over the whole RLC PDU. Theactual CRC check can be performed in the physical layer and the RLCentity receives the result of the CRC check together with data afterdeciphering the whole header and possible piggyback status informationcan be extracted from the RLC PDU. If the received PDU was a strongmessage or if the status information is piggybacked to an AM PDU, thecontrol information (status message) can be passed to the transmittingside which checks its retransmission buffer against the received statusinformation. The PDU number from the RLC header is used for deciphering550 and also when storing the ciphered PDU into the receive buffer. Onceall PDUs belonging to a complete SDU are in the receive buffer, the SDUcan be reassembled. Although not shown, checks for in sequence deliveryand duplicate detection can then be performed before the RLC SDU isdelivered to a higher layer.

When the User Equipment (UE) or mobile station moves between PTMtransmission and Point-to-Point (PTP) transmission (or changes cells),the RLC entity 152 is reinitialized. This can undesirably result in lossof any data sitting in Radio Link Control (RLC) buffers. As noted above,problems may arise when the mobile station moves from one cell toanother or when the delivery of Multimedia Broadcast and MulticastService (MBMS) content changes from a Point-to-Point (PTP) transmissionmode to Point-to-Multipoint (PTM) transmission mode in the serving cell.

It is desirable to preserve continuity of Multimedia Broadcast andMulticast Service (MBMS) during transitions between Point-to-Point (PTP)transmission and Point-to-Multipoint (PTM) transmission, or duringtransitions that occur between different cells (e.g., handover), and toavoid the submission of duplicate information. To preserve continuity ofMBMS service and to avoid the submission of duplicate information, theLayer 2 150 should be capable of re-aligning the data coming from thetwo streams. This synchronization cannot be provided by the physicallayer since the network terminating point might be different in eachmode. If Forward Error Correction (FEC) is performed below the RLC layer150, as is the case in 3GPP2, data can be lost during any transitionbetween Point-to-Multipoint (PTM) transmission and Point-to-Point (PTP)transmission, and vice-versa. In addition, this would require physicallayer synchronization and sharing of the same Medium Access Control(MAC) among multiple cells (e.g., having common scheduling). As such,this can cause problems in 3GPP2 where such assumptions do not apply.

Point-to-Point (PTP) Transmission

Assuming that the application has a significant delay tolerance, themost efficient data transfer mode for Point-to-Point (PTP) transmissionsis Radio Link Control (RLC) Acknowledged Mode (AM). For example, the RLCacknowledged mode (AM) is typically used for packet switched datatransfer over dedicated logical channels (PTP). The RLC operates inacknowledged mode (AM) on dedicated logical channels. As shown in FIG.5A, dedicated user traffic for one user service in the downlinkdirection can be sent through a logical channel known as the DedicatedTraffic Channel (DTCH).

In Acknowledged Mode (AM), the reverse link is available forretransmission requests if the data has errors. The RLC transmitsService Data Units (SDUs) and guarantees delivery to its peer entity bymeans of retransmission. If RLC can not deliver the data correctly, theuser of RLC at the transmitting side is notified. Operating in RLC AM isgenerally much more power efficient at the expense of introducingadditional delay.

Point-to-Multipoint (PTM) Transmission

The Common Traffic Channel (CTCH) is a unidirectional channel existingin the downlink direction and it can be used when transmittinginformation either to all terminals or a specific group of terminals.Both of these data transfer modes use unidirectional common channelsthat do not have a reverse-link channel set up.

It would be desirable to provide an architecture that allows MBMSservice to switch transparently between Point-to-Point (PTP) andPoint-to-Multipoint (PTM) modes of transmission. To obtain goodperformance when transitioning between Point-to-Point (PTP) andPoint-to-Multipoint (PTM) modes of transmission, it would also bedesirable to provide an architecture that allows switching betweendifferent Radio Link Control (RLC) modes. This can, for example, helpreduce power requirements.

Aspects of the present invention will now be described with reference toembodiments shown and described with reference to FIGS. 6 through 19.These features, can among other things, help to preserve servicecontinuity during such transitions by use of a new Forward ErrorCorrection (FEC) layer.

FIG. 6 is a diagram of a modified UMTS protocol stack having a ForwardError Correction (FEC) layer operable in a Forward Error Correction(FECd) mode and a Forward Error Correction (FECc) mode. The ForwardError Correction (FEC) layer allows the underlying Radio Link Control(RLC) entity 152 to change from one Radio Link Control (RLC) datatransfer mode to another Radio Link Control (RLC) data transfer modewhen the User Equipment (UE) changes from Point-to-Point (PTP)transmission to Point-to-Multipoint (PTM) transmission, whilemaintaining service continuity. According to this embodiment, the FECLayer can operate in a first mode (FECc) or in a second mode (FECd). Inone implementation, the first mode (FECc) can utilize parity blocks andthe second mode (FECd) can operate without parity blocks. The impact ofchanging between the FECd and FECc modes can be much lower than changingbetween RLC modes and can be seamless such that no data loss occursduring the transition.

The Forward Error Correction (FECc) mode can utilize outer-codingtechniques to protect user data. This can be particularly effective overcommon channels. The Forward Error Correction (FECc) mode allowsfunctionality typically found in the Unacknowledged Mode (UM), such asframing (segmentation and concatenation) and sequence number addition,to take place above the Radio Link Control (RLC) layer. As a result, theRadio Link Control (RLC) layer can use transparent mode (TM) forPoint-to-Multipoint (PTM) transmissions because traditionalUnacknowledged Mode (UM) functions can be performed at the Forward ErrorCorrection (FEC) layer. Although this functionality can be duplicated inRadio Link Control (RLC) Acknowledged Mode (AM), gains due to ARQ makeup for this duplication.

By positioning the Forward Error Correction (FEC) or outer-coding layerabove the Radio Link Control (RLC) layer, the sequence number can beadded in a layer which is independent of Radio Link Control (RLC). Useof additional overhead, such as sequence number, with unacknowledgedtransmissions can enable realignment of the Protocol Data Units (PDUs)with an Encoder Packet (EP) during asynchronous transmission of MBMSdata. Because the sequence numbers are added at a layer above Radio LinkControl (RLC), the sequence numbers are common in both Point-to-Point(PTP) transmission and Point-to-Multipoint (PTM) transmission, andtherefore when a transition occurs from Point-to-Multipoint (PTM)transmission to Point-to-Point (PTP) transmission, continuity ofsequence numbers can be maintained. This allows data to be realigned sothat duplication of data and/or missed data can be avoided.

Outer coding could also be used in Point-to-Point (PTP) transmission,which could potentially gain the system some power and/or reduce thedelay for retransmissions. Multimedia Broadcast and Multicast Service(MBMS) data can be delay tolerant to an extent. In Point-to-Point (PTP)transmissions, a feedback path is provided. This makes use of Radio LinkControl (RLC) Acknowledged Mode (AM) more efficient due to use of ARQretransmissions when needed that are generally more radio efficient thanan FEC scheme in which additional parity blocks are always sent. Assuch, addition of parity blocks to the MBMS payload data is unnecessaryon dedicated logical channels, for example, Point-to-Point (PTP).

FIGS. 7A and 7B show embodiments of a protocol structures of the accessstratum that include a forward error correction (FEC) layer 157 disposedabove the Radio Link Control (RLC) layer 150. An embodiment of theForward Error Correction (FEC) layer is described with reference to FIG.11.

The Forward Error Correction (FEC) layer 157 receives user-planeinformation 163 directly over the user plane radio bearers. Because theForward Error Correction (FEC) layer sits on top of the Radio LinkControl (RLC) layer, FEC-Protocol Data Units (PDUs) correspond to theRLC-Service Data Units (SDUs). The FEC layer preferably supportsarbitrary SDU sizes (constrained to multiples of 8 bits), variable-ratesources, out-of-sequence reception of packets from lower layers, andreception of duplicate packets from lower layers. FEC PDU sizes can beconstrained to multiples of 8 bits.

As described in greater detail below with reference to FIG. 9A, the FEClayer 157 segments and concatenates higher layer blocks of user data,such as SDUs, into equal size rows. Each row can also be referred to asan inner block. Each Protocol Data Unit (PDU) may include overhead. Theoverhead may include Length Indicators (LIs) that indicate the beginningof the last Protocol Data Unit (PDU) where data from a particular blockof user data, such as a Service Data Unit (SDU), can be located. Thecollection of PDUs comprise an Encoder Packet (EP) or “encoder matrix.”The number of PDUs included in an Encoder Packet (EP) depends, amongother factors, on the outer-code that is used. Packing each encoder“matrix” row into an independent or separate Transmission TimingInterval (TTI) can enhance physical layer performance. To reducebuffering burdens, shorter Transmission Timing Interval (TTI) durationscan be used.

The Encoder Packet (EP) can then be passed through an outer-code encoderto generate the parity rows. As will be described in greater detailbelow with reference to FIG. 9A, the FEC layer 157 may performouter-coding by providing the functionality of a Reed Solomon (RS) coderin the UMTS Terrestrial Radio Access Network (UTRAN) 20 and may performouter-decoding by providing the functionality of a Reed Solomon decoderin the User Equipment (UE) 10.

The parity rows generated by the outer encoder can be added to theEncoder Packet (EP), and placed in a transmission buffer as a group ofinner blocks. Each inner block has information added to it to produce aProtocol Data Unit (PDU). The group of PDUs can then be transmitted.

This FEC layer 157 also allows for the recovery of data belonging to asingle EP, even if different inner blocks are received from differentcells. This can be achieved through the transmission of a SequenceNumber (SN) in the header of each Protocol Data Unit (PDU). In oneembodiment, a System Frame Number (SFN) this can help maintain dataalignment relative to the Encoder Packet (EP). Sequence numbers arediscussed in greater detail throughout this document, for example, withreference to FIGS. 10A and 10B.

The FEC layer 157 may also perform padding and reassembly; transfer ofuser data; and perform in-sequence delivery of upper layer PDUs,duplicate detection, and sequence number checks.

In the embodiments shown in FIGS. 6 through 7A, the Forward ErrorCorrection (FEC) layer 157 is shown between the Packet Data ConvergenceProtocol (PDCP) layer 156 and Radio Link Control (RLC) layer 150 (e.g.,at the same level as (BMC) layer and below the Packet Data ConvergenceProtocol (PDCP) layer). By placing the Forward Error Correction (FEC)layer 157 just above the Radio Link Control (RLC) layer 150, performanceof the outer code can be optimized since the inner block size matchesthe “gold” packet size of the packets that are sent over the air.Nevertheless, it should be appreciated that the Forward Error Correction(FEC) layer is shown here only for purposes of illustration and notlimitation. Packet Data Convergence Protocol (PDCP) layer 156 may beused on top of Forward Error Correction (FEC) layer 157 for its headercompression capabilities. It should be noted that currently the PacketData Convergence Protocol (PDCP) layer 156 is defined for Point-to-Point(PTP) transmission that uses dedicated logical channels. As shown inFIG. 7B, the Forward Error Correction (FEC) layer may be providedanywhere within the Access Stratum above the Radio Link Control (RLC)layer or in the application layer. The Forward Error Correction (FEC)layer may be below or above the Packet Data Convergence Protocol (PDCP)layer. If FEC is performed at the application layer 80, it can applyequally to GSM and WCDMA even though the “gold” packet size would bedifferent for the two.

Outer Code Design

The new Forward Error Correction (FEC) layer can perform outer-coding onuser plane information. FIG. 8 is a diagram that shows an informationblock 91 and an outer code block 95 to illustrate the concept of outerblock code structures. FIG. 9A is a diagram showing an example of howouter code block structures can be applied to Multimedia Broadcast andMulticast Service (MBMS) data 91. Outer-coding can improve physicallayer performance when broadcasting delay-tolerant content over anentire cell. Outer codes can, for example, help avoid loss of dataduring transition between cells and during transitions betweenPoint-To-Point (PTP) transmission mode and Point-To-Multipoint (PTM)transmission mode.

An outer code block 95 can be represented in the form of a matrix thatincludes k Protocol Data Units 91 and N-k parity rows 93. In outer blockcoding, data can be assembled into large encoder packet or informationblock 91 by organizing user data into k payload rows by segmenting,concatenating, and padding data (including insertion of over head intoinner blocks), and then encoding the resulting information block 91 togenerate N-k parity rows 93 that can be added to the information block91 to produce an outer code block 95. The parity blocks 93 addredundancy information to the information block 91. The individual rowsof the outer code block can then eventually be transmitted over singleor multiple Transmission Timing Intervals (TTIs). Redundancy informationfor the set of Protocol Data Units (PDUs) can allow the originalinformation to be reconstructed even if some of the PDUs are lost duringtransmission.

FIG. 9A shows an exemplary outer code structure known as a Reed-Solomon(RS) block code. Reed-Solomon (RS) codes can be used to detect andcorrect channel errors. The outer-code shown in FIG. 9A is a systematic(n,k) block code, where each Reed-Solomon (RS) code symbol comprises abyte of information defined by a row and a column. Each column comprisesa Reed-Solomon (RS) code word. If n lost blocks are to be recovered,then at least n parity blocks are required. As such, the amount ofmemory required increases as the number of parity blocks increases. InReed-Solomon (RS) coding, N-k parity symbols can be added to the ksystematic symbols to generate a code word. In other words, a code wordof a Reed-Solomon (RS) code [N,k] has k information or “systematic”symbols and N-k parity symbols. N is the length of the code, and k isthe dimension of the code. For every k information bytes, the codeproduces n coded symbols, the first k of which can be identical to theinformation symbols. Each row can be referred to as an “inner block,”and represents the payload per Transmission Timing Interval (TTI). Inregular WCDMA systems, transmission may occur, for example, over thebasic WCDMA structure of 20 ms frames (TTIs). The parity symbols can bederived from the systematic symbols using a generator matrix G_(k×N·)defined as:m _(1×k) ·G _(k×N) =C _(1×N)  (Equation 1)m _(1×k)=Information word=[m ₀ m ₁ . . . m _(k-1)]  (Equation 2)c _(1×N)=Code word=[c ₀ c ₁ . . . c _(N-1)]  (Equation 3)where m_(i), c_(i) belong to an arbitrary Galois Field. For example, ifthe symbol of a Reed-Solomon (RS) code word is a bit, then the GaloisField of dimension 2 (GF(2)) would be used to describe the decodingoperations. In one embodiment, if the symbol is an octet, then theGalois Field of dimension 256 GF(256) can be used to describe thedecoding operations. In this case, each information column consists of1-byte per row. Each information column can be encoded using a [N, k]Reed-Solomon (RS) code over the Galois Field of dimension 256 GF(256).If there are M-bytes per row, the outer block is encoded M times.Therefore, there are N*M bytes per outer block 95.Erasure Decoding

The outer code structure allows for erasure correction. If the decoderalready knows which symbols are in error, the reconstruction of theerroneous systematic symbols requires a relatively little amount ofcomputation. An encoder packet (EP) or matrix refers to the entire setof data at the output of the outer encoder. Redundancy information istaken column wise from each row, and each row that is transmitted has aCRC appended to it that must check to confirm that the data has beensent correctly. In the case of MBMS transmissions, a CRC can be used ineach transport channel block that indicates whether an inner block 91 isin error or not, and if the CRC fails, it can be assumed that all thesymbols in the block are in error. In an embodiment, if a given innerblock 97 is in error, then all bits for that block can be erased. Theterm “erasure” refers to each symbol belonging to an erroneous blockwhose CRC has failed. Symbols, which are not erasures, can be assumedcorrect. Neglecting the CRC undetected error probability, then each N×1column contains correct and erased symbols.

The received vector r can be written as:r _(1×N) =[c ₀ eec ₃ c ₄ e c ₆ c ₈ . . . c _(N-1)]  (Equation 4)where e identifies the erasures.

Erasure decoding allows up to N-k erroneous symbols to be corrected.Because symbols, which are not erasures, can be assumed to be correct,the error correction property of RS codes is typically much better thanthat of typical RS codes. The size of the CRC used in each inner blockshould be large enough to ensure that the probability of undetectederrors does not exceed the residual outer block probability. Forexample, if a 16 bit CRC is used in the inner blocks, then the lowerbound of the residual outer block error rate will be 2⁻¹⁶=1.5·10⁻⁵. Ifthere can be no errors in the first k inner blocks, the RS decoding neednot be performed since the systematic symbols are identical to theinformation symbols.

It can be noted that as soon as k blocks with good CRCs are received,the decoding of the outer block can be performed, without waiting forthe reception of all the N inner blocks. In order to perform erasuredecoding, the modified generator matrix Ω_(k×k) can be derived from thegenerator matrix G_(k×N) by removing all the columns corresponding toerasures or unnecessary blocks, for example, only the first k goodreceived symbols can be used to identify the modified generator matrixΩ_(k×k). The original information word m can be recovered as follows:m _(1×k)=[Ω_(k×k)]⁻¹ ·ŕ _(1×k)  (Equation 5)where ŕ_(1×k) is the modified received vector obtained with the first kgood symbols. The erasure decoding complexity can therefore be reducedto the complexity of a k×k matrix inversion. Thus, use of RS erasuredecoding can greatly simplify the computational complexity of RSdecoding.Impact of Data Packing on Outer Code Performance

As will be discussed below with reference to FIGS. 11-13, outer-codingmay be used in conjunction with variable-rate data sources withoutresulting in exceedingly large overhead if the amount of padding andoverhead sent over the air is limited by the particular outer-codingscheme. In the outer-code scheme discussed above, data can be packedinto blocks of a given size, and a shortened Reed-Solomon code can berun across the blocks. The encoded packet data can be packed into TTIsin at least two different ways that will now be described with referenceto FIGS. 9A and 9B.

FIG. 9B is a diagram showing the outer code block structure of FIG. 9Ain which multiple rows can be sent per Transmission Time Interval (TTI).According to another aspect of the invention, the data from one row istransmitted in a single TTI. In another embodiment, data from oneEncoder Packet (EP) row is put into one TTI such that each TTI containsdata from that Encoder Packet (EP) row. As such, each of the rows can betransmitted in a separate WCDMA frame or Transmission Timing Interval(TTI). Transmitting each row in one TTI will provide better performance.In FIG. 9B, both k and n are divided by the number of rows per TTI, andthe errors in a row can be totally correlated. This creates anappreciable difference when looking at the EP error rate versus the TTIerror rate.

FIG. 9C is a diagram showing the outer block structure of FIG. 9A inwhich each row can be sent in multiple TTIs. It should be appreciatedthat while FIG. 9C illustrates sending each row of the Encoder Packet(EP) over four TTIs (TTI0-TTI3), in reality each row could be sent overany number of TTIs. Since each column is an outer code code-word, eachof the four distinct transmission “phases” (TTI0-TTI3) amounts to anindependent outer code. In order for the entire packet to be recoveredit would be necessary that all of these independent outer codes decodecorrectly.

FIGS. 10A and 10B are diagrams that show the outer code blocks generatedby the Forward Error Correction layer.

The FECc mode can be used on common or Point-to-Multipoint (PTM) logicalchannels to construct outer case blocks 95 by adding parity rows orblocks 93 to the MBMS payload data 91. Each outer block 95 includes aplurality of inner blocks 91, 93. Identifying the sequence of innerblocks and their position relative to encoder packets can allow eachavailable inner block to be placed in the correct position so thatouter-decoding can be done correctly. In one embodiment, each innerblock includes a header 94 that identifies the inner block by an innerblock number m and an outer block number n. For example, outer block nincludes a data portion 91 with m inner Multimedia Broadcast andMulticast Service (MBMS) payload blocks, and a redundancy portion 93having M−(m+1) inner parity blocks. According to this embodiment, thesequence number space can be optimized for MBMS and can be defined by anumber of distinct sequence numbers, for example, 0 through 127. Thesequence number space should be big enough so that the same sequencenumber will not appear after a reception gap caused by a transition ofany kind. The receiving UE should be able to determine the order of theinner blocks, even if some inner blocks are lost. If the UE loses moreinner blocks than can be identified by the whole sequence number space,the UE will not be able to reorder the inner blocks correctly. Thesequence number of the same inner block is identical across the FECdblocks and FECc blocks. The FECd blocks do not include the redundancyportion 93 utilized in the FECc blocks. The FECd entity and FECc entitymay use the same bit rate over the air.

Transmitting Side

The transmitting Forward Error Correction (FEC) entity 410 includes aService Data Unit (SDU) buffer 412 for receiving SDUs, a segmentationand concatenation unit 414, an outer encoder 416 that performsReed-Solomon (RS) encoding, a sequence number generator 418 that adds asequence number to the encoded PDUs, a transmit buffer 420 transmits thePDUs over the logical channels 406, and a scheduling unit 422.

The Service Data Unit (SDU) buffer 412 receives user data (FEC SDUs) inthe form of Service Data Units (SDUs) on radio bearer 402 as indicatedby the arrow, and stores FEC SDUs from the higher layers. The receivebuffer 412 communicates to the scheduling unit 422 how much data will betransmitted.

As discussed above, the amount of time it takes to fill-up an EncoderPacket (EP) will typically vary since the source data-rate typicallyvaries. As explained with reference to FIG. 13, frame-fill efficiencycan be improved by having flexibility in deciding when to start packingthe data. The amount of padding introduced can be reduced by delayingthe creation of the EP as much as possible based on the jitter toleranceof the receiving FEC entity 430.

The scheduling entity 422 can decide when to start the encoding. Thescheduler 422 preferably determines how long it is possible to waitbefore a packet needs to be sent out, based on QoS profile for thatparticular service. Once the scheduler 422 establishes that enough datahas accumulated, or that the maximum acceptable packet transmissiondelay has been exhausted, it triggers the creation of an Encoder Packet(EP) 91. The segmentation and concatenation unit 414 splits the ServiceData Unit (SDU) into the various rows and generates the LengthIndicators (LIs).

The scheduling unit 422 preferably decides the optimal row size of theEP or Protocol Data Unit (PDU) so that the SDUs fit exactly into thenumber of rows (e.g., 12). Alternatively, the scheduler 422 selects anFEC PDU size, from of those configured by the RRC, that will result inthe least possible padding, and requests that the Segmentation &Concatenation function 414 formats the SDUs into k blocks of sizePDU_size-FEC_Header_size. This formatting can vary. Examples ofdifferent types of formatting are discussed below with reference toFIGS. 12-13. The total amount of data considered should include theoverhead that will be incorporated by the concatenation and segmentationfunction 414. To generate the Encoder Packet (EP), the scheduler 422requests that the concatenation and segmentation function 414 produce kPDUs of that size. This size includes re-assembly information. In oneembodiment, the PDUs can have sizes in multiples of 8 bits, and the dataof consecutive PDUs correspond to different symbols in the code-words.

The k PDU blocks can then be run through the outer encoder 416 whichperforms, Reed-Solomon (RS) encoding. The outer encoder 416 encodes thedata in the Encoder Packet (EP) matrix by generating and appendingredundancy or parity information to the Encoder Packet (EP) matrix tocreate an outer code block. In an embodiment, the outer-code can beassumed to be an (n, k) erasure-decoding block code and the outerencoder generates n-k parity blocks. The encoder performs the encodingon k rows of information of equal length and delivers to the lowersub-layer n Protocol Data Units (PDUs) of that same size. The first kblocks are identical to the ones it receives, and the following n-kblocks correspond to the parity information.

The scheduler 422 also monitors time alignment or relative timing of PTMstreams, and performs transmissions to adjust the alignment of differentlogical streams. For example, during re-configurations, the timealignment between PTP and PTM logical streams can be adjusted to benefitthe service continuity. The best performance can be obtained when thestreams are perfectly synchronous.

Different base stations (or different modes of transmission PTP,Point-to-Multipoint (PTM)) transmit the same content stream, but thestreams can be misaligned. However, if the Encoder Packet (EP) format ofthe data streams is the same, then the information on each stream isexactly the same. Adding a sequence number to each outer block allowsthe User Equipment (UE) to combine the two streams since the UserEquipment (UE) will know the relationship between the two streams.

The sequence number generator 418 appends a sequence number at the frontof each block, in the same sequence as what was used in the encoder 416to create PDUs. In an embodiment, the sequence number generator adds,for example, an eight bit sequence number at the front of each outercode block to generate PDUs. Additional overhead information can also beadded to the outer code block. The sequence number space should be largeenough to accommodate the worse case time-difference between streams.Therefore, in another embodiment, a sequence number space of 20 can beused, and at least 5 bits can be reserved in each header for thesequence number. This header can be appended to the outer code blockafter the Reed-Solomon (RS) encoding is performed, and therefore this“outer” header is not protected by the outer-code. Sequence numbers arepreferably also added to for parity blocks, even if they can not betransmitted. In one embodiment, the sequence number phase can be alignedwith the encoder packet boundary. A sequence number roll-over wouldcorrespond to the reception of a new encoder packet.

Forward Error Correction (FEC) Header Format

As noted above, synchronization of data streams can be achieved byintroducing a sequence number that includes information associated withthe PDU ordering. In addition to re-ordering and duplicate detection,the sequence number allows the data from respective sources that areincluded in an encoder packet to be realigned. This sequence number canexplicitly identify the order in which each packet should be considered.This sequence number can make up an “FEC header” that can be appended toboth information Payload Units (PDUs) and parity blocks after theencoding is performed. The sequence number should not be protected bythe outer-code since it is needed for the decoding.

FIG. 14 is a diagram of an embodiment of a Forward Error Correction(FEC) header format. To facilitate alignment of the data with theEncoder Packet (EP), the sequence number can be split to include areserved portion (R) 402, a Encoder Packet (EP) portion 404 thatidentifies the EP (EPSN), and an intra Encoder Packet that identifiesthe location of a particular inner block within the Encoder Packet(IEPSN) 406.

It is desirable for the FEC layer 400 to be able to inter-operate withall Radio Link Control (RLC) modes. Since Radio Link Control (RLC) AMand Radio Link Control (RLC) UM both require Service Data Units (SDUs)to have sizes in multiples of 8 bits, then it would be desirable for theFEC layer 400 to also adhere to this requirement. Because the outer-codefor the FEC layer 400 operates on byte size increments of data, theEncoder Packet (EP) row size would also need to be an integer number ofbytes. Hence, the FEC header size 401 should also be a multiple of 8bits for the FEC Protocol Data Unit (PDU) size to be acceptable forRadio Link Control (RLC). In one embodiment in which the Forward ErrorCorrection (FEC) header 401 can be one byte, with a reserved portion (R)402 comprising a single bit, the portion that identifies the EP (EPSN)404 comprising 3 bits, and the IEP portion that identifies the locationof the PDU within the Encoder Packet (IEPSN) 406 comprising 4 bits. Inthis embodiment, an 8 bit sequence number is used since it is expectedthat one PDU will be sent per TTI and since the transmission timing ofdifferent cells is not expected to drift by more than 100 ms.

The transmit buffer 420 stores the PDUs until a frame of dataaccumulates. When the PDUs are requested, the transmit buffer 420transmits the frames one by one over the radio interface (Uu) via alogical channel to MAC layer. The MAC layer then communicates the PDUsvia transport channels to the physical layer where the PDUs can beeventually communicated to the UE 10.

Receiving Side

Still referring to FIG. 11, the receiving Forward Error Correction (FEC)entity 430 includes a receive buffer/reordering/duplicate detection unit438, a sequence number removal unit 436, an outer decoder 434 thatperforms Reed-Solomon (RS) decoding, and a reassembly unit/Service DataUnit (SDU) transmit buffer 432.

Information rows of the EP matrix correspond to PDUs. To support outercoding the receiving Forward Error Correction (FEC) entity 430accumulates a number of FEC PDUs before triggering the outer decoding.To achieve continuous reception, despite the need to decode encoderpackets, the User Equipment (UE) buffers the incoming Protocol DataUnits (PDUs) while performing the decoding.

The receive buffer 438 may accumulate PDUs until the entire EncoderPacket (EP) is received or until the scheduling unit (not shown) issatisfied that there are no more retransmissions for the Encoder Packet(EP). Once it is decided that there will be no more data received for agiven encoder-packet, missing PDUs can be identified as erasures. Inother words, PDUs that did not pass the CRC test will be replaced byerasures in the de-coding process.

Because some blocks could be dropped during transmission, and alsobecause different data streams may have different delays, the receivingForward Error Correction (FEC) entity 430 performs duplicate detectionand potentially re-ordering of received blocks in the receivebuffer/reordering/duplicate detection unit 438. The sequence number canbe used in each FEC Protocol Data Unit (PDU) to assist withreordering/duplicate detection. The sequence number can be used in thereceive buffer 438 to reorder the data received out of order. Once PDUsare reordered, the duplicate detection unit detects duplicate PDUs inthe Encoder Packet (EP) based on their sequence numbers, and eliminatesany duplicates.

The sequence numbers can then be removed. The sequence number removalunit 436 removes the sequence number from the Encoder Packet (EP) sincethe sequence number can not be part of the block sent to theReed-Solomon (RS) decoder.

The data can then be passed to the outer-decoding function 434 torecover missing information. The outer decoder 434 receives the EncoderPacket (EP), and, if necessary, Reed-Solomon (RS) decodes the EncoderPacket (EP) by using the parity information to regenerate any erroneousor missing rows. For example, if all k Protocol Data Units (PDUs)containing information are not received correctly, or fewer than k outof n PDUs are not received correctly, then the Protocol Data Units(PDUs), up to the size of the parity PDUs, outer decoding can then beperformed to recover the missing information PDUs. At least one parityPDU will be available at the receiver whenever outer decoding isperformed. If all k Protocol Data Units (PDUs) containing informationare received correctly, or fewer than k out of n PDUs are receivedcorrectly, then decoding is unnecessary. The information Protocol DataUnits (PDUs) can then be delivered to the re-assembly function 432.

Independently of whether the outer decoding was successful or not, theinformation rows can then be delivered to the re-assembly unit/function432. The reassembly unit 432 reassembles or reconstructs the SDUs fromthe information rows of the Encoder Packet (EP) matrix using the LengthIndicators (LIs). Once SDUs are successfully put together, the ServiceData Unit (SDU) transmit buffer 432 transmits the Service Data Units(SDUs) over the radio bearer 440 to deliver the SDUs to the higherlayers.

At the receiving Forward Error Correction (FEC) entity 430, enabling UEsto delay the decoding by a time-offset between different logical streamscan allow the system to take full advantage of potential out-of-sequencereception of data due to lack of synchronization between logicalstreams. This smoothes out service during hand-offs as well astransitions between PTP and PTM. An algorithm for enabling UEs to delaythe decoding by the time-offset between different logical streams isdiscussed with reference to FIG. 15.

Encoder Packet (EP) Options: Fixed or Variable Row Size

The FEC or outer-code entity has flexibility as to when Protocol DataUnits (PDUs) can be constructed since the Protocol Data Units (PDUs) donot need to be sent continuously at every Transmission Timing Interval(TTI). This can result in better frame-fill efficiency, and less paddingoverhead.

If desired, the outer-code entity can generate a payload at eachTransmission Timing Interval (TTI). Protocol Data Units (PDUs) can beconstructed in real-time as Service Data Units (SDUs) can be receivedfrom the higher layers. If there is not enough data to build a ProtocolData Unit (PDU), then the RLC can add padding.

Fixed Row Size Encoder Packets (EPs)

When encoding the SDUs 201-204 it is desirable to reduce amount ofpadding that will be transmitted as much as possible.

In one embodiment, the row size of the Encoder Packet (EP) matrix 205may be of a fixed size. A priori knowledge of the Encoder Packet (EP)matrix 205 row size can allow alignment of the data back to theiroriginal configuration. Because the row size of SDUs 201-204 that willbe sent within is known in advance, transmission can start as soon asthe data is received without waiting to see how much data is to be sent.

FIG. 12A shows an example of an encoding process for creating an outercode block 214 from data units 201-204 in which row sizes of the outercode block 214 can be fixed. In this example, user data takes the formof a plurality of Service Data Units (SDUs) 201-204 that include anarbitrary size block of bits, the size of which depends upon theparticular application (video, voice, etc.).

In order to be able to transmit FEC SDUs of arbitrary sizes,segmentation, concatenation and padding can be performed at FEC level.Although concatenation is not strictly necessary, its absence would leadto significant degradation in higher layer data throughput.

The higher layer SDUs 201-204 can first be formatted into this fixed PDUsize. In this embodiment, a segmentation/concatenation functiongenerates inner blocks of a fixed size that can be indicated to thesubscriber unit. At step 220, the group of inner blocks can be segmentedand concatenated to become part of an encoder packet matrix 205 thatincludes inner blocks, padding 208 to the extent necessary, and lengthindicators (LIs) 206 that can be used to point to an end of the ServiceData Unit (SDU) 201-204 by indicating how many SDUs end in a given rowof the EP. The outer encoder, discussed below, uses these inner blocksto produce redundancy blocks.

In the Radio Link Control (RLC), a Length Indicator (LI) indicates theend of each Service Data Unit (SDU) which is identified relative to theProtocol Data Unit (PDU), rather than the Service Data Unit (SDU). Thishelps in reducing the overhead since the PDU size is typically smallerthan that of the Service Data Unit (SDU). For example, a LengthIndicator (LI) can be used to indicate the last octet of each FECService Data Unit (SDU) ending within the Payload Data Unit (PDU). The“Length Indicator” can be set to the number of octets between the end ofthe FEC header and up to the last octet of an FEC SDU segment. TheLength Indicator (LI) can be preferably included in the PDUs that thatLength Indicator (LI) refers to. In other words, the Length Indicators(LIs) preferably refer to the same Payload Data Unit (PDU) and arepreferably in the same order as the FEC SDUs that the Length Indicator(LI) refers to.

When the outer block is received, information, such as Length Indicators(LIs), can be used to let the receiver know where the Service Data Unit(SDU) and/or padding start and end.

Because it is not possible to use a bit in the FEC Header to indicatethe presence of a Length Indicator (LI), the FEC layer adds a fixedheader within the payload that indicates the presence of LengthIndicators (LIs). An inner header or LI provides all the informationneeded for re-constructing the SDUs 201-204. The LI can be included inthe RLC-PDU to which it refers. The presence of the first LI can beindicated by a flag included in the sequence number header of theRLC-PDU. A bit in each LI can be used to indicate its extension. Toallow the length of the Length Indicators (LIs) to change with FEC PDUsize, a new special value for the one byte Length Indicators (LIs) maybe introduced indicating that the previous SDU ended one byte short offilling the last PDU. The Length Indicators (LIs) presence bit can beimplemented in a variety of ways, two of which are discussed below.

In one embodiment, a Length Indicator (LI) presence bit can be providedin each protocol data unit (PDU). For example, a byte can be added atthe beginning of each Encoder Packet (EP) row, and a bit in that byteindicates the presence of the LI. The entire first byte of each ProtocolData Unit (PDU) may be reserved for this “presence bit.” In order toaccommodate this presence bit, the length indicator data can beshortened by one bit. Providing a presence bit in each Pocket Unit (PDU)allows SDUs to be decoded when the EP decoding fails, even if the firstPDU is missing. This can result in lower residual error rate. Providinga presence bit in each PDU also allows for real-timeconcatenation/segmentation.

In another embodiment, a Length Indicator (LI) presence bits can beprovided in the first PDU. Instead of adding the overhead at thebeginning of each PDU, the presence bits for all k information PDUs canbe added at the beginning of the first PDU of the EP. Providing thepresence bit at the beginning of Encoder Packet (EP) results in lessoverhead when having large SDUs and/or small PDUs.

After segmentation and concatenation, the EP 205 includes a number ofrows occupied by at least one of the plurality of Service Data Units(SDUs) 201-204 and padding blocks. The row size of an outer block can bedesigned so that each row can be transmitted during one TransmissionTiming Interval (TTI) at a peak data rate. Service Data Units (SDUs)generally can not be aligned with the amount of data sent during aTransmission Timing Interval (TTI). Thus, as shown in FIG. 11, thesecond and fourth SDUs 202, 204 do not fit into the Transmission TimingInterval (TTI) of first and second rows, respectively, of the EP. Inthis example, the EP has 12 rows available for data, and the four SDUs201-204 can be packed into the first three rows of these 12 rows. Theremaining rows of the EP 205 can be occupied by padding blocks 208.Thus, the second SDU 202 can be split so that a first portion of thesecond Service Data Unit (SDU) 202 starts in the first row of“information block” and a second portion of the second SDU 202 ends inthe second row. Similarly, the third SDU must be split so that a firstportion of the third Service Data Unit (SDU) 203 starts in the secondrow and a second portion of the third SDU 203 ends in the third row. Thefourth Service Data Unit (SDU) 204 fits within the third row, and theremainder of the third row can be filled with padding blocks 208. Inthis example, the Encoder Packet (EP) 213 is mostly made up of padding208.

The encoder uses the EP to generate redundancy or parity information. Atstep 240, an encoder encodes the intermediate packet matrix 205 encodedby adding outer parity blocks 214 to generate an outer code block 213that is 16 blocks in length. The encoder extracts 8 bits of data fromeach column of each block to create resulting data 210. A Reed-Solomon(RS) encoder encodes the resulting data 210 to obtain four rows ofredundancy or parity information 212. The parity information 212 can beused to generate outer parity blocks 214 that can be appended to the EPmatrix 205 to generate the 16 block outer code block 213.

FIG. 12B shows an example of the information transmitted over the air inthe example discussed above. At step 260, after adding additionaloverhead that includes the sequence number to each row of the EP 205,the 16 block outer code block 213 can be transmitted over the air asProtocol Data Units (PDUs) 214. The full or entire Encoder Packet (EP)213 matrix is not transmitted in the Protocol Data Units (PDU) 214 senton the downlink. Rather, the Protocol Data Units (PDU) include theinformation bits 201-204 and the length indicators (LIs) 206 of theEncoder Packet (EP) matrix 213. Since the Encoder Packet (EP) 213 rowsize is fixed and therefore known at the receiver, it is unnecessary toactually transmit the padding 208 over the air. Padding information 208is not transmitted on the downlink since the padding values are known,and therefore there is no need to transmit the padding information 208.For example, if the padding can be made up of a known sequence of bitssuch as all zeros, all ones, or an alternate pattern of zeros and ones,the receiver can pad the Protocol Data Units (PDUs) 214 up to thenominal Encoder Packet (EP) 213 row length. Therefore, duringtransmission, instead of selecting the PDU size equal to the EP rowsize, the smallest available EP size that carries all the informationbits 201-204 and re-assembly overhead (e.g., LIs) 206 can be utilized.

Although the encoder matrix row size is fixed, the FEC PDU size could beselected from a given set at each transmission such that each includesall the information part of a single encoder matrix row (the paddingcould be excluded). When receiving a PDU of size smaller than theencoder matrix row size, the UE can pad up to that size with a known bitsequence. This allows the inner block size to remain fixed, withoutincreasing the load on the air interface. Using a fixed row size EncoderPacket (EP) 213 can thus eliminate the need to wait until all the datais available before starting to transmit Protocol Data Units (PDUs), andcan also eliminate the need to send padding.

If the algorithm above is implemented to handle variable ratetransmission, then a rate equalization scheme can be used in which allencoder packet matrix rows have constant size. Smaller PDUs could beused when padding makes up part of the PDU. The padding can be made upof a specific bit sequence, and can be located at the very end of thedata. At the receiver, the size of the blocks received from the lowerlayers can be equalized to a base-line size by appending padding at theend.

If a predefined sequence of bits can be used for padding, this paddingis not transmitted over the air. The receiver does not need to know theactual encoder packet row size unless the receiver needs to run theouter-decoding. Basic SDU re-assembly does not require knowledge of theamount of padding at the end of a PDU. If all the PDUs containinginformation from the first k Encoder Packet (EP) rows are received, thenouter decoding is unnecessary. By contrast, if at least one PDUscontaining information from the first k Encoder Packet (EP) rows ismissing, then at least one of the PDUs containing the data from a parityrow is needed. Since parity rows not generally padded, the size can beused as a reference for the actual encoder packet size that needs to beassumed.

Variable Row Size Encoder Packets (EPs)

FIG. 13 shows an encoding process for creating an outer code block 313having a variable row size.

This aspect of the invention relates to flexible outer block coding ofdata transmitted over the air interface. This encoding process resultsin less padding being transmitted so that frame fill efficiencyincreases. The Encoder Packet (EP) 305 rows can be variable size, and adifferent sized outer block can be sent for each Transmission TimingInterval (TTI). Preferably, the row size of the Encoder Packet (EP) 305changes such that the SDUs fit exactly into the number of rows (e.g.,12) of the Encoder Packet (EP) matrix 305. In this embodiment, the FEClayer must wait for all of the data to be available before building theEP so that the FEC layer may determine the optimal row size. The rowsize can be selected from a number of different sizes based on theamount of data available so as to limit padding. The row size of theEncoder Packet (EP) can be linked to the set of PDU sizes that areconfigured for the S-CCPCH. Depending on the amount of data available atthe time when the encoder packet 305 needs to be generated, the row sizethat results in the least padding can be selected. By decreasing thesize of the outer block 313 so that the block size can be smaller ineach frame, data can be sent at a reduced transmission rate since lessdata is sent over the same TTI duration. Using a variable row size ofthe Encoder Packet (EP) 305 helps stabilize power requirements acrossall transmissions for Encoder Packets (EPs), and also utilizes lessparity overhead 314. This embodiment works well with Point-to-Multipoint(PTM) transmissions in systems such as WCDMA in which the underlyingwireless protocol allows the size of the transport block sent in eachTransmission Timing Interval (TTI) to be varied.

At step 320, a plurality of Service Data Units (SDUs) 201-204 can besegmented and concatenated to generate an Encoder Packet (EP) matrix 305in which length indicators (LIs) 206 can be used to point to an end ofthe Service Data Unit (SDU) 201-204. Length Indicators (LIs) can beincluded in the last row in which each Service Data Unit (SDU)terminates.

At step 330, redundancy or parity information is generated on a columnbasis by extracting eight bits of data from each data block, and theresulting data 310 can be sent to a Reed-Solomon (RS) encoder to obtainparity information 312. Because the rows of the Encoder Packet (EP)matrix 305 are smaller, less redundancy information can be generated.

At step 340 encoding continues, as the parity information 312 is used togenerate outer parity blocks 314 that can be appended to the twelveblock Encoder Packet (EP) matrix 305 to thereby generate an outer codeblock that in this example is 16 blocks in length. This embodimentavoids padding transmission which improves transmission efficiency sincethe entire outer code block 313 is occupied by either SDUs, LengthIndicators (LIs) 206, and/or redundancy information 314. In thisspecific example no padding was needed. It should be appreciated that,however, in some cases because the number of configured sizes of the PDUwill be limited, and some padding may be needed albeit a reduced amountof padding. This results in greater frame fill efficiency, and can alsoallow a more constant power to be maintained across the entire EncoderPacket (EP). This is desirable in CDMA systems that utilize powercontrol schemes.

Although not shown, transmission of PDUs over the air would occur in amanner similar to that discussed above with respect to step 260 of FIG.12.

FIG. 11 is an embodiment of an outer coding or Forward Error Correction(FEC) layer 400 having a RLC Unacknowledged Mode (UM)+entity (RLC UM+)provided above the Radio Link Control (RLC) layer. Typically, the RadioLink Control (RLC) provides framing for higher layers. Here, the FEClayer that sits above Radio Link Control (RLC) performs framing.

The outer coding layer 400 includes a transmitting Forward ErrorCorrection (FEC) entity 410 that communicates over the radio interface(Uu) 404, via logical channels 406, with a receiving Forward ErrorCorrection (FEC) entity 430.

Re-Ordering/Duplicate Detection

FIG. 15 is a re-ordering protocol or algorithm for enabling mobilestations 10 to delay decoding by the time-offset between differentlogical streams.

The receiving Forward Error Correction (FEC) entity 430 uses thesequence number to determine the position of a given PDU within the EPmatrix. For example, a part of the sequence number (PSN) identifies theposition of the PDU in the Encoder Packet (EP).

This algorithm assumes that, at most, data from two encoder packets (EP)are received before decoding can be initiated. In the description below,the Encoder Packet (EPd) is the next Encoder Packet (EP) in sequence tobe decoded, and the Encoder Packet (EPb) is the Encoder Packet (EP) thatis being buffered. The Encoder Packet (EPb) follows Encoder Packet(EPd). UE implementations needing the full encoder packet transmissiontime to perform the RS decoding will need to do double-buffering inorder to be able to decode sequential packets. The UE therefore storesat least n+k of the maximum size rows of the encoder matrix (k and nbeing respectively the number of information rows and the total numberof rows including parity ones). A UE having a faster decoding engine canreduce this requirement, though no lower than n+1. For example, if theUE has a certain amount of buffer space (XtraBffr) beyond that needed toreceive sequential packets based on its decoding capability, and if a 64kbps stream is assumed, delaying the decoding by 100 ms withoutincreasing the computational requirements would require an 800 byteincrease in buffer size.

At block 1410, it can be determined whether a new Forward ErrorCorrection (FEC) Protocol Data Unit (PDU) is received. If a new ForwardError Correction (FEC) Protocol Data Unit (PDU) is not received, thenthe process restarts at block 1410. If a new Forward Error Correction(FEC) Protocol Data Unit (PDU) is received, at block 1420 adetermination can be made whether the new Forward Error Correction (FEC)Protocol Data Unit (PDU) belongs to the next Encoder Packet (EPd) insequence to be decoded.

If the Forward Error Correction (FEC) Protocol Data Unit (PDU) does notbelong to the next Encoder Packet (EP) in sequence to be decoded, thenat block 1421, a determination can be made whether the Forward ErrorCorrection (FEC) Protocol Data Unit (PDU) belongs to the Encoder Packet(EPb) that is being buffered. If the Forward Error Correction (FEC)Protocol Data Unit (PDU) does not belong to the Encoder Packet (EPb)that is being buffered, then at block 1440 the Protocol Data Unit (PDU)can be discarded. If the Forward Error Correction (FEC) Protocol DataUnit (PDU) does belong to the Encoder Packet (EPb) that is beingbuffered, then at block 1423 the Protocol Data Unit (PDU) can be addedto the buffer of EPb in the associated position. At block 1425, it canbe determined whether the amount of data for EPb exceeds XtraBffr. If atblock 1426 it is determined that the amount of data for EPb does notexceed XtraBffr, then the process restarts at block 1410. If the amountof data for EPb exceeds XtraBffr, then at block 1428, the transmittingentity attempts to deliver complete SDUs from EPd. Then, at block 1430,the remainder of EPd can be flushed from the buffer, and at block 1434EPb can be set to EPd.

If it is determined at block 1420 that the Forward Error Correction(FEC) Protocol Data Unit (PDU) belongs to EPd, then at block 1422, theProtocol Data Unit (PDU) can be added to the buffer of EPd in theassociated position. At block 1424, it can be determined whether thebuffer has k individual PDUs for EPd. If the buffer does not have kindividual PDUs for EPd, then at block 1426, the process restarts atblock 1410. If the buffer does have k individual PDUs for EPd, then atblock 1427 the decoder performs outer decoding for EPd, and then atblock 1428, the transmitting entity attempts to deliver complete SDUsfrom EPd. Then, at block 1430, the remainder of EPd can be flushed fromthe buffer, and at block 1434 EPb can be set to EPd.

FIG. 16 is a diagram that shows a temporal relationship between outercode blocks received by a mobile station as the mobile stationtransitions between receiving a Point-To-Multipoint (PTM) transmissionfrom cell A 99 and another Point-To-Multipoint (PTM) transmission fromcell B 99. Some aspects of FIG. 16 are discussed further in U.S. patentapplications US-2004-0037245-A1 and US-2004-0037246-A1 to Grilli, etal., filed Aug. 21, 2002, and U.S. patent application US-2003-0207696-A1to Willenegger, et al., filed May 6, 2002, which are hereby incorporatedby reference in their entirety.

The scenario depicted assumes certain UMTS Terrestrial Radio AccessNetwork (UTRAN) 20 and User Equipment (UE) 10 requirements. For example,if the UTRAN 20 sends content using the same outer block coding acrosscells, then the same numbering should be used on blocks carrying thesame data or payload in neighbor cells. Outer blocks of the same numberhave are transmitted relatively time-aligned. The maximum misalignmentof PTM transmission across the cells is controlled by the Radio NetworkController (RNC) 24. The UTRAN 20 controls the delay jitter onPoint-to-Multipoint (PTM) transmission across cells. The UE 10 should becapable of decoding an outer block while the next one is being received.Therefore, a buffer space in the UE should preferably accommodate atleast two outer blocks 95A-95C since memory for one outer block isneeded to accumulate the current outer block. Memory should also becapable of accumulating inner blocks of “rows” if the outer blocksduring Reed-Solomon (RS) decoding, and to compensate for inaccuracies inthe time alignment across base stations 22.

In cell A 98, during transmission of outer block n 95A, a transitionoccurs during transmission of the second inner Multimedia Broadcast andMulticast Service (MBMS) payload block. The slope of arrow 96, whichillustrates the User Equipment (UE) 10 transition from cell A 98 to cellB 99, is non-horizontal since some time elapses during the transition.By the time the User Equipment (UE) 10 reaches cell B 99, the fifthblock of Multimedia Broadcast and Multicast Service (MBMS) payload datais being transmitted. As such, the User Equipment (UE) 10 misses thesecond through fourth blocks due to the time misalignment of therespective transmissions and the time that elapses during thetransition. If enough blocks are received in cell B 99, the outer blockn 95A may nevertheless be decoded because the parity blocks can beutilized to reconstruct the missed blocks.

Later, during the transmission of outer block n+2 95C, the UserEquipment (UE) 10 experiences another transition from cell B 99 to cellA 98, that occurs at the fifth inner Multimedia Broadcast and MulticastService (MBMS) payload block of outer block n+2 95C. In this situation,fewer inner blocks are lost during the transition, and the outer blocksmay still be recovered.

The use of outer code blocks can help reduce the likelihood of anyservice interruption. To ensure that the error recovery will work, thesame blocks should be sent on each transmission path which means thatthe parity blocks should be constructed in the same way in eachtransmission path. (The Multimedia Broadcast and Multicast Service(MBMS) payload blocks are necessarily the same in each path since it isa broadcast transmission.) Performing Forward Error Correction (FEC) atthe upper application layer 80 helps ensure that the parity blocks willbe identical in each transmission path since the encoding is done in theForward Error Correction (FEC) layer 157 and is therefore the same foreach outer block. By contrast, if encoding is done in a lower layer, forexample, at the individual Radio Link Control (RLC) entities 152, thensome coordination is required since the parity blocks would be differentin each transmission path.

Transition from Point-to-Multipoint (PTM) to Point-to-Point (PTP)

FIG. 17 is a diagram that shows a temporal relationship between outercode blocks received by a mobile station 10 as a transition between aPoint-To-Multipoint (PTM) transmission and a Point-To-Point (PTP)transmission occurs. The scheme shown in FIG. 17 applies, for example,to systems that utilize Point-to-Point (PTP) transmissions, such asWCDMA and GSM systems.

An aspect of the present invention relates to forward error correctionby adding parity information or blocks to inner MBMS “payload” or datablocks during PTM transmission. Each outer code block transmitted in aPTM transmission comprises at least one inner payload block and at leastone of inner parity block. The error correcting capabilities of outercode blocks can significantly reduce and tends to eliminate the loss ofMBMS content or “payload” during transitions, such as when the UE movesfrom one cell to the other, or when the delivery of MBMS content changesfrom a PTM connection to a PTP connection in the same serving cell, andvice-versa.

As noted above, a given cell can transmit to a subscriber 10 usingeither a PTP or a PTM transmission scheme. For example, a cell thatnormally transmits a broadcast service in a PTM transmission mode maychoose to set up a dedicated channel and transmit in a PTP mode (only toa certain subscriber 10) if the demand within that cell for the servicefalls below a certain threshold. Likewise, a cell that normallytransmits content on a dedicated channel (PTP) to individual subscribersmay decide to broadcast the content to multiple users over a commonchannel. In addition, a given cell might transmit content in PTPtransmission mode whereas another cell might transmit the same contentin a PTM transmission mode. A transition occurs when the mobile station10 moves from one cell to another, or when the number of subscriberswithin a cell changes triggering a change in the transmission schemefrom PTP to PTM or vice-versa.

During a Point-to-Multipoint (PTM) transmission of outer block n 95A, atransition occurs during transmission of the fourth inner MultimediaBroadcast and Multicast Service (MBMS) payload block. The slope of arrow101, which illustrates the User Equipment (UE) transition from aPoint-to-Multipoint (PTM) transmission to a Point-to-Point (PTP)transmission, is non-horizontal since some time elapses during thetransition. When a transition from PTM 101 to PTP occurs, theover-the-air bit rate remains approximately the same. Point-to-Point(PTP) transmissions typically have a bit error rate of less than onepercent (e.g., during transmission there is one error or less in every100 payload blocks). By contrast, in Point-to-Multipoint (PTM)transmission a higher bit error rate can be assumed. For example, in oneembodiment, the base station generates an outer block once for every 16transmission time intervals (TTIs), and twelve of these TTIs can beoccupied by payload blocks and four TTIs can be occupied by parityblocks. The maximum number of block errors that can be tolerated shouldbe 4 inner blocks out of 16 (12 fundamental blocks +4 parity blocks). Assuch, the maximum tolerated block error rate would be ¼.

When the mobile station transitions 101 from a Point-to-Multipoint (PTM)transmission to Point-to-Point (PTP) transmission, some of the innerblocks can be lost. Assuming that Point-to-Multipoint (PTM)transmissions and Point-to-Point (PTP) transmissions have approximatelythe same bit rate at the physical layer (L1), then the PTP transmissionwill allow the MBMS payload blocks to be sent faster than PTMtransmission since, on average, the percentage of retransmitted blockswould typically be lower than the percentage of parity blocks. In otherwords, Point-to-Point (PTP) transmissions are typically much faster thanPoint-to-Multipoint (PTM) transmissions since, statistically speaking,the number of parity blocks is much larger than the number of Radio LinkControl (RLC) retransmissions (Re-Tx). Because the transition 101 isfrom a Point-to-Multipoint (PTM) transmission to Point-to-Point (PTP)transmission that is typically much faster, when the User Equipment (UE)10 transitions 101 to a Point-to-Point (PTP) transmission, the firstblock of Multimedia Broadcast and Multicast Service (MBMS) payload datais being transmitted. As such, neither the time misalignment of therespective transmissions, nor the time that elapses during thetransition 101, causes any of the blocks to be missed. Therefore, whenmoving from Point-to-Multipoint (PTM) transmission to Point-to-Point(PTP) transmission, the lost payload block may be made up by simplyrestarting from the beginning of the current outer block once the PTPlink has been established on the target cell. The network can compensateby starting PTP transmission from the beginning of the same outer block,i.e. with the first inner block. The network can then recover the delayintroduced by the transition due to the faster delivery of completeouter blocks. Reducing loss of data during transitions reducesinterruptions in delivery of MBMS content that can be caused by suchtransitions.

Later, during the PTP transmission of outer block n+2, the UserEquipment (UE) 10 undergoes another transition 103 to aPoint-to-Multipoint (PTM) transmission mode. In FIG. 12, this transition103 from Point-to-Point (PTP) to Point-to-Multipoint (PTM) occurs at thelast inner Multimedia Broadcast and Multicast Service (MBMS) payloadblock of outer block n+2. In this situation, many of the innerMultimedia Broadcast and Multicast Service (MBMS) payload blocks inouter block n+2 have already been transmitted except for the last innerblock. FEC is typically utilized in situations where feedback is notavailable. Because PTP transmissions utilize a dedicated channel, andtherefore have feedback capability on the reverse link, use of FEC isnot as beneficial. In order to minimize or eliminate the loss of data inthe cross transitions, UMTS Terrestrial Radio Access Network (UTRAN) 20preferably relies on the low residual block error rate of the RLCAcknowledged Mode (AM) in PTP transmission to recover all the innerblocks that could be lost during a transition to PTM transmission. Inother words, normal layer 2 retransmissions can be utilized toretransmit any packets in which error(s) are detected in the originaltransmission. Thus, as shown in FIG. 17, parity blocks are not needed inPTP transmissions. If errors are present in the payload blocks during aPoint-to-Point (PTP) transmission, the outer block may nevertheless bedecoded because the Radio Link Control (RLC) layer will requestretransmission of any erroneous blocks. That is, when there is an errorduring the PTP transmission, the mobile station 10 either requestsretransmission (re-Tx) or when all of the blocks are correct, noretransmission takes place and a transport format zero (TF0) can beutilized. Outer coding is preferably done in layer 2 of the protocolstack so that the size of each inner block 97 fits exactly into oneTransmission Timing Interval (TTI) since this can enhance codingefficiency.

If Forward Error Correction (FEC) outer coding is done at an upper layerof the protocol stack such as the application layer, then parity blockswill be sent regardless of the transmission scheme (Point-to-Point (PTP)or Point-to-Multipoint (PTM)). As such, parity blocks would also beappended to Point-to-Point (PTP) transmissions.

As noted above, in PTP transmission the use of parity blocks is notnecessary, since more efficient retransmission schemes can be used inlieu of forward error correction. Since parity blocks are preferably nottransmitted in PTP transmission, the delivery of a complete outer blockcan be on average faster than in PTM, assuming the same bit rate overthe air. This allows the UE to compensate for the interruptions causedby the Point-to-Multipoint (PTM) to Point-to-Point (PTP) transitions,since the PTP transmission can be anticipated with respect to the PTMtransmission. The User Equipment (UE) can recover the outer blockcorrectly by combining (1) inner blocks received in Point-to-Point (PTP)transmission, either in the new cell or after transition, with (2) innerblocks received in Point-to-Multipoint (PTM) transmission, either in theold cell or before transition. The User Equipment (UE) can combine innerblocks received before the transitions and inner blocks received afterthe transition that belong to the same outer block. For example, UserEquipment (UE) 10 can combine the inner Multimedia Broadcast andMulticast Service (MBMS) payload blocks in outer block n+2 that arereceived via Point-to-Point (PTP) transmission with the inner MultimediaBroadcast and Multicast Service (MBMS) payload blocks in outer block n+2and parity blocks that are received via Point-to-Multipoint (PTM)transmission. UMTS Terrestrial Radio Access Network (UTRAN) 20 canfacilitate this process by slightly “anticipating” the transmission ofouter blocks to all the users that receive MBMS content from PTP linkswith respect to the transmission on PTM links.

Because the UTRAN anticipates the transmission of outer blocks withrespect to the PTM transmission, “seamless” transitions from PTP to PTMare possible. As a result, delivery of MBMS content across cell bordersand/or between different transmission schemes such as PTM and PTP isalso “seamless.” This “time anticipation,” can be expressed in number ofinner blocks. When the User Equipment (UE) 10 transitions to a PTMtransmission, even if a communication link does not exist during thetransition time, the User Equipment (UE) 10 can lose up to “timeanticipation” number of inner blocks without compromising the QoS of theMBMS reception. If the UE starts MBMS reception directly in PTP, theUTRAN could apply the “time anticipation” immediately at the beginningof the PTP transmission since the UTRAN 20 can slowly anticipate thetransmission of outer blocks by avoiding empty inner blocks (TF 0),until the anticipation reaches the required “time anticipation” numberof inner blocks. From that point onward, UTRAN can keep the “timeanticipation” constant.

In Point-to-Multipoint (PTM), UE specific feedback information availablein the Radio Network Controller (RNC) can not be relied upon. In thePoint-to-Point (PTP) transmission, the UE 10 could inform the RNC of thenumber of last outer block correctly received before the transition.This should apply to any transition to PTP (from PTM or from PTP). Ifthis feedback is not deemed acceptable, UTRAN 20 can estimate the lastouter block that was most likely received by the User Equipment (UE) 10before the state transition. This estimate could be based on theknowledge of the maximum time inaccuracy foreseeable between distinctcell transmissions, and based on the outer block currently beingtransmitted or that will soon be transmitted in the target cell.

The Forward Error Correction (FEC) can be performed so that any blockslost during the transition can be recovered. This results in a“seamless” transition by reducing the likelihood that content will belost during a transition. This scheme assumes that the transition fromPoint-to-Point (PTP) to Point-to-Multipoint (PTM) transmission occurswhile the same outer block is being transmitted from each source, whichtypically occurs given the duration of an outer block with respect tothe duration of a transition.

The amount of memory in the UE 10 can be traded off with the accuracy inthe time alignment of PTM transmissions across neighboring cells. Byrelaxing the memory requirement in the User Equipment (UE) 10, the timeaccuracy of PTM UTRAN 20 transmissions can be increased.

FIG. 18 is a diagram that shows a temporal relationship between outercode blocks received by a mobile station during a transition orrelocation between a Point-To-Point (PTP) transmission from RadioNetwork Controller (RNC) A and another Point-To-Point (PTP) transmissionfrom Radio Network Controller (RNC) B. The term RNC can be usedinterchangeably with the term “Base Station Controller (BSC).” During a“relocation” the User Equipment (UE) 10 transitions from aPoint-to-Point (PTP) transmission of a content stream in an areacontrolled by a first RNC A 124 to Point-to-Point (PTP) transmission ofthe same content stream in an area controlled by a second RNC B 224.Retransmissions (re-Tx) can be used to compensate for any missed MBMSpayload blocks. The direct transition from Point-to-Point (PTP) toPoint-to-Point (PTP) between cells can be performed similarly to aRelease '99 soft handover or hard handover. Even without coordinationbetween the two RNCs A,B, the target RNC A 124 should be able to figureout the latest whole outer block received by the UE 10. This estimatecould be based on the timing of the MBMS content received by the RNC 24on the Iu interface 25. When using PTP transmission, the RNC 24 can makeup an initial delay, and no part of the MBMS content will be lost evenwithout requiring lossless SRNS relocation.

One skilled in the art will appreciate that although the flowchartdiagrams can be drawn in sequential order for comprehension, certainsteps can be carried out in parallel in an actual implementation.Furthermore, unless indicate otherwise, method steps can me interchangedwithout departing form the scope of the invention.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality can be implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium can be coupled to the processor such theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. For example, although the descriptionspecifies that the radio access network 20 can be implemented using theUniversal Terrestrial Radio Access Network (UTRAN) air interface,alternatively, in a GSM/GPRS system, the access network 20 could be aGSM/EDGE Radio Access Network (GERAN), or in an inter-system case itcould be comprise cells of a UTRAN air interface and cells of a GSM/EDGEair interface. Thus, the present invention is not intended to be limitedto the embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

What is claimed is:
 1. A system for transmitting information blocks,comprising: a destination station comprising a decoder, the decoderconfigured to receive particular content from a first source andtransition to receive a remainder of the particular content from asecond source; the first source of the particular content transmittingfirst outer blocks for receipt by the destination station, the firstouter blocks including information blocks and redundancy blocksgenerated above the radio link control layer that can be used toreconstruct the information blocks; the second source of the particularcontent transmitting second outer blocks comprising information blocksfor receipt by the destination station when the destination stationundergoes the transition between the first source and the second source,wherein the decoder is further configured to reconstruct any informationblocks of the second outer blocks lost during the transition and avoiddecoding duplicate information blocks using the redundancy blocks; andwherein the transmission rate of the information blocks from the secondsource of the particular content is greater than the transmission rateof the information blocks from the first source of the particularcontent, and wherein the second source of the particular content startstransmission at a first information block of the first outer block beingtransmitted when the transition occurs to thereby reduce loss ofinformation blocks during the transition.
 2. A system according to claim1, wherein the second source of the particular content retransmits asecond outer block over a dedicated channel if any information blocksfrom the second outer block are not received correctly during anothertransition from the second source of the particular content to the firstsource of the particular content.
 3. A system according to claim 1,wherein each block occupies one frame.
 4. A system according to claim 1,wherein the destination station is further configured to combine theinformation blocks received from the first source of the particularcontent and the information blocks received from the second source toproduce the complete outer block, when the transition occurs while thesame outer block is being transmitted from each source.
 5. A systemaccording to claim 1, wherein the first source of the particular contentincludes a Reed-Solomon encoder that encodes the information blocks togenerate the redundancy blocks, and adds the redundancy blocks to theinformation blocks to generate outer code blocks.
 6. A system accordingto claim 1, wherein the first outer blocks comprise sequence numbersidentifying a sequence of inner blocks within the first outer blocks andthe second outer blocks comprise corresponding sequence numbers forinner blocks of the second outer blocks, the decoder configured tocombine the first outer blocks with the second outer blocks using thesequence numbers.
 7. A system for transmitting information blocks,comprising: a destination station comprising a decoder; a first sourceof a particular content that transmits first outer blocks over a commonchannel for receipt by the destination station using a first datatransfer mode, wherein the first outer blocks include information blocksand redundancy blocks that can be used to reconstruct the informationblocks, wherein the redundancy blocks are generated above a radio linkcontrol layer; and a second source of the particular content thattransmits second outer blocks comprising information blocks over adedicated channel for receipt by the destination station using a seconddata transfer mode when the destination station undergoes a transition,wherein the second outer blocks are aligned with corresponding firstouter blocks, wherein the decoder is configured to: receive particularcontent from the first source and transition to receive a remainder ofthe particular content from the second source; reconstruct anyinformation blocks lost during the transition using the redundancyblocks; and avoid decoding duplicate information blocks using theredundancy blocks, and wherein the transmission rate of the informationblocks from the second source of the particular content is greater thanthe transmission rate of the information blocks from the first source ofthe particular content, and wherein the second source of the particularcontent starts transmission at a first information block of the firstouter block being transmitted when the transition occurs to therebyreduce loss of information blocks during the transition.
 8. A systemaccording to claim 7, wherein the second source of the particularcontent retransmits a second outer block over the dedicated channel ifany information blocks from the second outer block are not receivedcorrectly during another transition from the second source of theparticular content to the first source of the particular content.
 9. Asystem according to claim 7, wherein each block occupies one frame. 10.A system according to claim 7, wherein the destination station isfurther configured to combine the information blocks received from thefirst source of the particular content and the information blocksreceived from the second source to produce the complete outer block whenthe transition occurs while the same outer block is being transmittedfrom each source.
 11. A system according to claim 7, wherein the firstsource of the particular content includes a Reed-Solomon encoder thatencodes the information blocks to generate the redundancy blocks, andadds the redundancy blocks to the information blocks to generate outercode blocks.
 12. A system according to claim 7, wherein the outerdecoder decodes the first outer code block and reproduces any missinginformation blocks via said redundancy blocks.